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Published byJesse McNeil Modified over 3 years ago

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Making Molar Solutions From Solids

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What are molar solutions? A molar solution is one that expresses concentration in moles per volume Usually the units are in mol/L mol/L can be abbreviated as M or [ ] Molar solutions are prepared using: a balance to weigh moles (as grams) a volumetric flask to measure litres L refers to entire volume, not water! Because the units are mol/L, we can use the equation M = n/L Alternatively, we can use the factor label method

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Calculations with molar solutions Q: How many moles of NaCl are required to make 7.5 L of a 0.10 M solution? But in the lab we weigh grams not moles, so … Q: How many grams of NaCl are required to make 7.5 L of a 0.10 M solution? M=n/L, n = 0.10 M x 7.5 L = 0.75 mol # mol NaCl = 7.5 Lx 0.10 mol NaCl 1 L = 0.75 mol # g NaCl = 7.5 Lx 0.10 mol NaCl 1 L =43.83 g x g NaCl 1 mol NaCl Read pages 288 – 290. Do Q

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19. # g NaOH = 3.00 Lx mol NaOH 1 L =15.0 g x g NaOH 1 mol NaOH 20. # g NaCl = 5.0 Lx 0.56 mol NaCl 1 L = 164 g x g NaCl 1 mol NaCl ppm = 355 mg/L or g/L 22.a) 235 g 3000 mL x 100% =7.83 % W/V b) mol/L = 4.02 mol / 3.00 L = 1.34 mol/L # g CO 2 = 1.00 Lx g CO 2 1 L =.355 g x 1 mol CO g CO 2 = 8.07 x 10 –3 mol 1L = 8.07 x 10 –3 mol/L g CO 2

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Practice making molar solutions 1.Calculate # of grams required to make 100 mL of a 0.10 M solution of NaOH (see above). 2.Get volumetric flask, plastic bottle, 100 mL beaker, eyedropper. Rinse all with tap water. 3.Fill a beaker with distilled water. 4.Pour mL of H 2 O from beaker into flask. 5.Weigh NaOH. Add it to flask. Do step 5 quickly. 6.Mix (by swirling) until the NaOH is dissolved. 7.Add distilled H 2 O to just below the colored line. 8.Add distilled H 2 O to the line using eyedropper. 9.Place solution in a bottle. Place label (tape) on bottle (name, date, chemical, molarity). Place bottle at front. Rinse & return equipment.

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More Practice Questions 1.How many grams of nitric acid are present in 1.0 L of a 1.0 M HNO 3 solution? 2.Calculate the number of grams needed to produce 1.00 L of these solutions: a) 1.00 M KNO 3 b) 1.85 M H 2 SO 4 c) 0.67 M KClO 3 3.Calculate the # of grams needed to produce each: a) 0.20 L of 1.5 M KCl b) L of M HCl c) 0.20 L of 0.09 mol/L AgNO 3 d) 250 mL of 3.1 mol/L BaCl 2 4.Give the molarity of a solution containing 10 g of each solute in 2.5 L of solution: a)H 2 SO 4 b)Ca(OH) 2 5.Describe how 100 mL of a 0.10 mol/L NaOH solution would be made. 63 g 101 g 181 g 82 g a) 22 gb) 1.75 g c) 3 g d) 0.16 kg a) mol/L b) mol/L For more lessons, visit

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