How many moles of CF_4 are there in 171 g of CF_4? 0.51 mol 1.94 mol 4.07 mol 88

Question

How many moles of CF_4 are there in 171 g of CF_4? 0.51 mol 1.94 mol 4.07 mol 88.0 mol 171 mol What mass of K_2CO_3 is needed to prepare 200. mL of a solution having a potassium ion concentration of 0.150 M? 4.15 g 10.4 g 13.8 g 2.07 g 1.49 g Which of the following characteristics indicates the presence of weak intermolecular forces in a liquid? a low heat of vaporization a high critical temperature a low vapor pressure a high boiling point none of these the solubility of CO_2 gas in water increases with increasing temperature. decreases with decreasing temperature. decreases with increasing temperature. is not dependent on temperature. Which two properties are more typical of molecular compounds than of ionic compounds? They are gases or liquids at room temperature. They have high melting points. Solids do not conduct electricity, but liquids do. Atoms share electrons. 1 and 4 1 and 3 2 and 3 2 and 4 3 and 4 Which of these elements is most likely to be a good conductor of electricity? N S He Cl Fe

Explanation / Answer

(55)

Number of moles = mass / molar mass = 171 / (12+4(19)) = 171 /88 = 1.94 mol

(56) K2CO3 (aq.) -------------> 2 K+ (aq.) + CO32- (aq.)

Conc. of K2CO3 = 1/2 concentration of K+ = 1/2 (0.150) = 0.0750 M

Volume of solution = 200. mL = 0.200 L

Molarity = moles of solute / volume of solution in L

Moles of solute = 0.0750 * 0.200 = 0.015 mol

Mass of K2CO3 = 0.015 [2(39) + 12 + 3 (16)] = 2.07 g.

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