4. A student adds an excess (more than she needs to react completely) of solid s

Question

4. A student adds an excess (more than she needs to react completely) of solid sodium hydrogen carbonate to a

beaker containing exactly 675 mL of 0.220M coper(II)nitrate aqueous solution. A reaction occurs that produces

solid copper(II)carbonate, carbon dioxide gas, liquid water, and aqueous sodium nitrate.

a) Write a balanced chemical equation for the reaction.

b) What mass (g) of carbon dioxide gas will be produced?

5. In an experiment, you are instructed to make an aqueous solution that is 0.778 M potassium thiosulfate. You are

to use a 250.0-mL volumetric flask. What mass (g) of potassium thiosulfate do you need to weigh and add to the

flask to make this solution?

Explanation / Answer

4.

2 NaHCO3 + Cu(NO3)2 = CuCO3 +CO2 + H20 + 2 NaNO3

mol wt. of Cu(NO3)2 = 249.5g

1000 * n /675 = 0.22

n= 0.1485 moles

weight of Cu(NO3)2 in solution = 0.1485 * 249.5 = 37.05g

249.5 g of Cu(NO3)2 produce 44g of CO2

so 37.05 g will produce 44*37.05/249.5= 6.534 g of CO2.

5. mol wt. of K2S2O3 = 190.32 g

1000 * n/ 250 = 0.778

n = 0.1945 moles

x /190.32 = 0.1945

x = 37.02 g

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