A student adds 6.00 g of a solid to 30.0 mL of water. What is the concentration

Question

A student adds 6.00 g of a solid to 30.0 mL of water. What is the concentration of this solution expressed as mass/mass percent? (Assume that 1. 00 mL of water has a mass of 1. 00 g.) a. 20.09% (m/m) b. 0.200% (m/m) c. 0.167% (m/m) d. 16.7% (m/m) Calculate the grams of NaOH present in 9.0 mL of an 8.0% (m/v) NaOH solution. a. 8.0 g b. 0.80 g c. 0.72 g d. 7.2 g What is the concentration of calcium ions in 350. mL of an aqueous solution containing 7.50 g CaCl_2? a. 0.535 M b. 0.193 M c. 0.0676 M d. 0.284 M

Explanation / Answer

Question 18.

m = 6 g of solid

V = 30 mL

find concentration in mass/mass %

Recall that

D = mass/Volume

so

mass = D*V = (30*1) =)30 g of water

total mass = 30+6 = 36 g of solution

for mass / mass we need

% m/m = mass of solute / mass of solution * 100%

% m/m = 6/36 * 100% = 16.67%

choose D

Question 19.

m/V *100 %= 8%

mass = 8/100*9 = 0.72 g os sample

Question 20.

M = mol/V

mol = mass/MW = 7.5/110.98 = 0.06757 moles

M = 0.06757 / (0.35) = 0.193

choose B

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