2 1. Why did chemists develop the concept of molarity? To easily connect the amount in moles of a substance with its concentration in a solution
3 2. In what units is molarity expressed Moles per literMol/L
4 3. Describe in your own words how to prepare 100. 0 mL of a 0 3. Describe in your own words how to prepare mL of a 0.85 M solution of sodium chloride. 23Na + 36Cl= 59NaCl.85 mol NaCl x 59 g/mol = 50 g/L or 5.0g NaCl for 1/10 L (100ml)Weigh 5.0 g of salt, dissolve in water. Pour into 100 ml volumetric flask, swirl and fill to volumetric line
5 4. If you dissolve 2. 00 mol KI in 1. 00 L of water, will you get 2 4. If you dissolve 2.00 mol KI in 1.00 L of water, will you get 2.00 M solution? Explain.NoThe total volume may be different by the time the solute is dissolved.
6 5. A sample of 400. 0 g of water is found to contain 175 mg Cd 5. A sample of g of water is found to contain 175 mg Cd. What is this concentration in parts per million.Change mg to g175 mg x 1 g/ 1000 mg = .175 g CdFind g Cd/g of water.175 g/ g water x 1000,000 parts /1 million =or parts per million or ppm
7 1.63 parts per million or ppm He 6. If 1.63 x 10-4 g of helium dissolves in g of water, what is the concentration in parts per million?How much in 1 gram of water?1.63 x 10-4 g He / 100g H2O x 1000,000 parts/million1.63 parts per million or ppm He
8 A standard solution of NaOH is 1. 000 M A standard solution of NaOH is M. What mass of NaOH is present in mL of the solution?Na = 23, O = 16, H = 1 NaOH = 4040 g in 1 M100 mL is 1/10 Lso 40/10 = 4 g in mL
9 8. A 32 g sample of LiCl is dissolved in water to to form 655 mL of solution. What is the molarity of the solution?Convert mass to moles. Li = 6.9,Cl = 3632 g x mol/43g LiCl = .74 mol LiClConvert mL to L655 ml x 1 L/ 1000mL = .655 LFind Moles per Liter.74 mol / .655 L = or M LiCl
10 9. Most household bleach contains sodium hypochlorite, NaOCl. A 2 9. Most household bleach contains sodium hypochlorite, NaOCl. A 2.84 L bottle contains 177 g NaOCl. What is the molarity of the solution.Find moles of NaOCl Na=23,O=16,Cl=35.5177g NaOCl x mol/74.5g NaOCl = 2.38 Mol NaOClFind mol/L2.38 mol/2.84 L = or mol/L or M
11 10. What mass of AgNO3 is needed to prepare 250. 0 mL of a 0 10. What mass of AgNO3 is needed to prepare mL of a M solution.Ag=108,N=14,O3= 16(3)= 48 AgNO3 = 170 gM = g/L = 170g /mol = for 1 Mol solution170/4 for .250 L = 42.5 g for .250 L AgNO342.5 g for 1 M, 42.5 x .125 M5.25 or 5.3 g AgNO3 for .125 M solution
12 11. Calcium phosphate used in fertilizers can be made in the reaction described by the following equation: 2H3PO4(aq) + 3Ca(OH)2(aq) --> Ca3(PO4)2(s) + 6H2O(aq) Ca=40(3), P=31(2), O=16(8)=128, = 310g total H= 1(2), O=16, total 18g total What mass in grams of each product would be formed if 7.5 L of 5.00 M phosphoric acid reacted with an excess of calcium hydroxide?H3PO4 = 1(3) (4) or 64 = 98g for 1 M98x5 x 7.5 = 3,562.5 or g H3PO43600g 2H3PO4 x 1 mol/98g x 1 mol Ca3(PO4)2 /2mol 2H3PO4x310 g Ca3(PO4)2 /1 mol Ca3(PO4)2 = 5,693.8 or 5.7 x 103 Ca3(PO4)218g H2O
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