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Solutions

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**Solutions A solution is made up of a solute dissolved in a solvent.**

Example: seawater is a solution. It is made up of salt (the solute) dissolved in water (the solvent).

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**Solutions can be described as concentrated or dilute.**

A concentrated solution has a large amount of solute per solvent A dilute solution has a small amount of solute per solvent.

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**Concentration of solutions**

The concentration of a solution is the amount of solute dissolved in a certain amount of solvent.

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**1. Moles per litre Concentration can be measured in :**

moles of litre (mol L-1 ). This is also known as molarity. 1M solution = 1 mole in 1 litre = 1 mole in 1000cm3

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**2. Grams per litre Concentration can be measured in :**

Grams per litre of litre (g l-1 ). 1g l-1 solution = 1g in 1 litre = 1g in 1000cm3

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**How many moles in 1 litre of solution? 10g / RMM = moles **

Example 1 A solution contains 10g of Sodium Hydroxide in I litre of solution. What is the concentration expressed in moles per litre. Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass How many moles in 1 litre of solution? 10g / RMM = moles 10g / 40 = 0.25 There are 0.25 moles of NaOH in one litre. Answer = 0.25 mol L-1

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**There are 0.5 moles of KOH in one litre. Answer = 0.5 mol L-1**

Example 2 A solution contains 28g of Potassium Hydroxide (KOH) in I litre of solution. What is the concentration in moles per litre. Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 28g / RMM = moles 28 / 56 = 0.5 There are 0.5 moles of KOH in one litre. Answer = 0.5 mol L-1

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**There are 16g of MgSO4 in one litre.**

Example 3: A solution contains 48g of MgSO4 in 3 litres of water. What is the concentration in moles per litre. Given Grams per 3 litres GRAMS PER LITRE Find MOLES PER LITRE How many grams in 1L ? 48/ = 16 There are 16g of MgSO4 in one litre.

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**How many moles in 1 litre of solution?**

Given Grams per 3 litres GRAMS PER LITRE Find MOLES PER LITRE How many moles in 1 litre of solution? Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 16 / RMM = moles = 120 There are moles of MgSO4 in one litre. Answer = mol L-1

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Q219 Calculate the molarity of a solution which contains 65g of HCl in a litre Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 65 / rmm = moles 65 / 36.5 = moles in a litre Answer : M

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Q219b Calculate the molarity of a solution which contains 65g of HCl in a litre Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 25 / rmm = moles 25 / 56 = moles in 250cm3 x 4 = moles in a litre Answer : M

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Q219c Calculate the molarity of a solution which contains 22g of H2SO4 per 100cm3 of a solution Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 22 / rmm = moles 22 / 98 = moles in 100cm3 x 10 = moles in a litre Answer : M

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Q219d Calculate the molarity of a solution which contains 10g of NaOH per 2L solution Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 10 / rmm = moles 10 / 40 = 0.25 moles in 2L 0.25 /2 = moles in a litre Answer : M

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Q219e Calculate the molarity of a solution which contains 12.5g of Na2CO3 per 200cm3 solution Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 12.5 / rmm = moles 12.5 / 106 = moles in 200cm3 x 5 = moles in a litre Answer : M

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221 A chemist dissolves 98.4 g of FeSO4 in enough water to make up 2L of solution. What is the molarity of the solution? Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass 98.4 / rmm = moles 98.4 / 152 = moles in 2L / 2 = moles in a litre Answer : M

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**Q220 0.080g of ethanol in 100cm3 of blood**

0.080 x 10 = 0.8g of ethanol in 1L of blood 0.8/ RMM= Moles of ethanol 0.8/ 46 = moles in 1L Answer = M

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**Q223 Calculate the mass of NaOH in 20cm3 of 0.1M NaOH**

Moles of X Mass of X in g X Relative Molecular Mass ÷ Relative Molecular Mass Moles x rmm = mass 0.1 x 40 = 4.0g in 1L 4.0g /1000 = .004g in 1cm3 0.004 x 20 = 0.08 g in 20cm3 Answer :0.08g

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q223 B) 1.53g C)0.0158g D) 146g E)0.196g

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Q224 A) 40gl-1 B)112gl-1 C)12.25gL-1 D)1.06gl-1 E)0.49gl-1

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**There are 1.85g of Ca(OH)2 in one litre. Answer = 1.85gL-1**

Example 4 What is the concentration in grams per litre of a 0.025M solution of Ca(OH)2? Given Moles PER LITRE Find Grams PER LITRE (0.025)(74) There are 1.85g of Ca(OH)2 in one litre. Answer = 1.85gL-1

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**Example: What is the mass of CuSO4 in 250cm3 of a 3M solution?**

Given Moles PER LITRE Find Grams PER LITRE Grams per 250cm3 How many grams in 1 litre of solution? There are 478.5g of CuSO4 in one litre. Answer =478.5 gL-1

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**How many grams in 250cm3 litre of solution?**

Given Moles PER LITRE Find Grams PER LITRE Grams per 250cm3 How many grams in 250cm3 litre of solution? (478.5)/ 4 = Answer = grams in 1 litre = gl-1

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**3. Mass per volume Concentration is also measured in**

% mass of solute(g) per volume of solvent(cm3) This is written as % (w/v) 1% (w/v) means 1g of solute in 100cm3 of solvent 20% (w/v) means 20g of solute in 100cm3 of solvent

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**The solution of KOH has 70g in 500cm3 of water. **

Express the concentration in w/v% Answer: w/v means how many grams of KOH are in 100cm3 of water Given mass in 500cm3 Want mass in 100cm3 70g of KOH in 500cm3 of water You need to divide by 5! 70/5 = 14 14g of KOH in 100cm3 of solution Answer = 14w/v%

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**Express the concentration in w/v%**

Q225 .A solution of sodium chloride consists of 75 grams in a 250cm3 volume of water. Express the concentration in w/v% Answer: w/v means how many grams of NaCl are in 100cm3 of water Given mass in 250cm3 Want mass in 100cm3 75g of NaCl in 250cm3 75 / 250 x 100 = 30 30g of NaCl in 100cm3 of solution Answer = 30 w/v%

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4. Volume per volume Concentration is also sometimes measured in % volume of solute (cm3) per solvent (cm3) This is written as % (v/v) 5% (v/v) means 1cm3 of solute in 100cm3 of solvent

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**USE: This is used for expressing the alcohol content in wine**

11% written on a bottle of wine means 11cm3 of alcohol in 100cm3 of wine!

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**How many cm3 of ethanol are there is 30cm3 of the whiskey?**

The label on a bottle of whiskey says that the ethanol content is 40% (v/v). How many cm3 of ethanol are there is 30cm3 of the whiskey? Answer: 40%v/v means 40cm3 of ethanol in 100cm3 of whiskey Given volume in 100cm3 Want volume in 30cm3 x cm3 of ethanol = 30cm3 of whiskey 40cm3 of ethanol = 100cm3 of whiskey (30)(40) = (100)(x) 1200 = x 100 12 = x 12cm3 of ethanol in 30cm3 of whiskey

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**Q226. The label on a bottle of beer says that the ethanol content is 4**

Q226.The label on a bottle of beer says that the ethanol content is 4.8% (v/v). How many cm3 of ethanol are there in one pint 568cm3 of the beer? Answer: 4.8%v/v means 4.8cm3 of ethanol in 100cm3 of beer Given volume in 100cm3 Want volume in 568cm3 (568)(4.8) / (100) = cm3 of ethanol in 30cm3 of beer

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5. Mass per mass Concentration is also sometimes measured in % mass of solute(g) per mass of solvent(g) This is written as % (w/w) 36% (w/w) means 36g of solute in 100g of solvent

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**A solution has a w/w% concentration of 35%**

A solution has a w/w% concentration of 35%. What mass of solute would be present in 450g of solvent? Answer: 35% w/w means 35g of solute in 100g of solvent Given mass in 100g Want mass in 450g (35)/100 x 450 = ? (35)/100 x 450 = 157.5 157.5g of solute in 450g of solvent Answer: 157.5g

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**Q227. Concentrated hydrochloric acid is a 37**

Q227. Concentrated hydrochloric acid is a 37.9 (w/w)% solution of HCl in water. What mass of this solution would have to be taken so that it contains 5g of HCl? Answer: 37.9% w/w means 39.7g of solute in 100g of solvent Given mass in 100g Want mass of solvent with 5g of solute 37.9/ 100 = 0.379g in 1cm3 of solvent 5/0.379 = There would need to be g of solution Answer: g

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Standard solutions A standard solution is a solution whose concentration is accurately known

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**Primary Standard solution**

A primary standard is a water soluble substance that is stable and available in pure form. They are used to make standard solutions.

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**Examples of Primary Standards**

Sodium Chloride Examples of Primary Standards Potassium Dichromate Anhydrous Sodium Carbonate

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**Common substances that are not primary standards include:**

Sulfuric acid – absorbs water vapour from the air. Sodium hydroxide – absorbs water vapour from the air. Iodine – sublimes.

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**Preparation of a standard solution of sodium carbonate.**

We want to make up 250cm3 of a 0.1M solution of Na2CO3 What mass of sodium carbonate is needed??

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**How to make a standard solution**

A special technique is used so that the concentration of the solution can be accurately known! Find the mass of the solute accurately using a mass balance, and a clock glass.

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2. The solute is transferred to a clean beaker (filled with some deionised water) using a stirring rod

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3. A wash bottle (filled with deionised water) is used to rinse the clock glass and stirring rod into the beaker. The solution is stirred to dissolve the solute completely.

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**5. The solution from the beaker is poured into a volumetric flask**

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**6. Any solution remaining in the beaker is washed into the volumetric flask, using a wash bottle**

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7. The flask is filled up to close to the calibration mark with a wash bottle, and then drop wise until the bottom of the meniscus is at the calibration mark.

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**8. The flask is stoppered, and inverted 20 times to sure the solution is mixed properly!**

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**6. Expressing concentration in parts per million (ppm)**

ppm (parts per million) = milligrams in a litre

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**Convert the following to ppm 0.62g / 500cm3**

Given grams per 500cm Grams per 1000cm Need: mg per 1000cm3 0.62g in 500cm3 (0.62) / 500 x 1000 = 1.24g 1.24g in 1000cm3 To convert grams to milligrams 1.24 x 1000 = 1240 1240 mg in 1000cm3 Answer = 1240ppm

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**228(a)Convert the following to ppm 0.54g / 1L**

Grams per 1000cm Need: mg per 1000cm3 To convert grams to milligrams multiply by 1000 0.54g x 1000 = 540 540 mg in 1000cm3 Answer = 540ppm

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**228(b)Convert the following to ppm 0.18g / 1L**

Grams per 1000cm Need: mg per 1000cm3 To convert grams to milligrams 0.18g x 1000 = 180 180 mg in 1000cm3 Answer = 180ppm

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**228c)Convert the following to ppm 0.077g / 100cm3**

Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3 (0.077) x 10 = 0.77 0.77g in 1000cm3 To convert grams to milligrams (1000)(0.77) = 770 770 mg in 1000cm3 Answer = 770ppm

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**228d)Convert the following to ppm 0.0009g / 100cm3**

Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3 (0.0009) x 10 = 0.009 0.009g in 1000cm3 To convert grams to milligrams 0. 009g x 1000 = 9 9 mg in 1000cm3 Answer = 9ppm

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**228e)Convert the following to ppm 0.0017g / 100cm3**

Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3 (0.0017) x 10 = 0.017 0.017g in 1000cm3 To convert grams to milligrams 0. 017g x 1000 = 17 17 mg in 1000cm3 Answer = 17ppm

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**228f)Convert the following to ppm 0.0003g / 100cm3**

Given grams per 100cm Grams per 1000cm Need: mg per 1000cm3 (0.0003) x 10 = 0.003 0.003g in 1000cm3 To convert grams to milligrams 0. 003g x 1000 = 3 3 mg in 1000cm3 Answer = 3ppm

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colour of a solution If the solution is coloured then the more concentrated a solution the more intense the colour will be!! Colorimetry is when colour is used to measure the concentration of solutions

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**Effect of Dilution on Concentration**

When a solution is diluted, more solvent is added. The quantity of solute remains unchanged.

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