Practice Quiz - Thursday 1/22

Match the following...

• multiplying my avagadro's constant

• You convert moles to grams by...

• dividing by the molar mass

• You convert grams to moles by...

• multiplying by the molar mass

• You convert moles to particles by...

What is the molar mass of PbSO₄?

• 303.27 g/mol

• 255.27 g/mol

• 163.87 g/mol

• 372.27 g/mol

Answer explanation

To find the molar mass of PbSO4, sum the atomic masses: Pb (207.2 g/mol) + S (32.07 g/mol) + 4 x O (16.00 g/mol) = 303.27 g/mol. Thus, the correct answer is 303.27 g/mol.

How many molecules are there in 31.8 moles of water?

• 5.28 x 10^-23

• 1.91 x 10²⁵

• 5.28x 10-²⁵

• 1.91 x 10²²

Answer explanation

To find the number of molecules in 31.8 moles of water, multiply by Avogadro's number (6.022 x 10^23). Thus, 31.8 moles x 6.022 x 10^23 molecules/mole = 1.91 x 10^25 molecules, making the correct answer 1.91 x 10^25.

Determine the mass of 4.20 moles of C₆H₁₂

• 354 g

• 0.0499 g

• 337 g

• 2.53 x 10²⁴ g

Answer explanation

To find the mass of 4.20 moles of C6H12, first calculate its molar mass: C (12.01 g/mol) x 6 + H (1.008 g/mol) x 12 = 84.06 g/mol. Then, multiply by the number of moles: 4.20 moles x 84.06 g/mol = 353.88 g, rounded to 354 g.

Which of the following dimensional analysis setups will correctly convert 27.76 g of Li to atoms of Li?

• A

• B

• C

• D

Answer explanation

To convert grams of Li to atoms, use the molar mass of Li (6.94 g/mol) and Avogadro's number (6.022 x 10^23 atoms/mol). Choice D correctly sets up the conversion: 27.76 g Li x (1 mol Li/6.94 g) x (6.022 x 10^23 atoms/mol).

What is the mass of 1.2 x 10²⁴ atoms of C?

• 2.0 grams

• 24 grams

• 0.17 grams

• 1.4 x 10²⁵ grams

Answer explanation

To find the mass of 1.2 x 10^24 atoms of carbon (C), use the molar mass of carbon (12 g/mol). First, calculate moles: 1.2 x 10^24 atoms / 6.022 x 10^23 atoms/mol = 2 moles. Then, mass = 2 moles x 12 g/mol = 24 grams.

Calculate the number of atoms in 0.0340 g Zn.

• 5.20 x 10^-4 atoms Zn

• 3.13 x 10²³ atoms Zn

• 3.13 x 10²⁰ atoms Zn

• 2.05 x 10²² atoms Zn

Answer explanation

To find the number of atoms in 0.0340 g of Zn, first calculate moles: 0.0340 g / 65.38 g/mol = 0.000519 moles. Then, multiply by Avogadro's number (6.022 x 10^23): 0.000519 moles x 6.022 x 10^23 = 3.13 x 10^20 atoms Zn.

Tags

NGSS.HS-PS1-7

Which of the following dimensional analysis setups will correctly convert 4.00x10²³atoms of cobalt to moles of cobalt? How many moles of colbalt are there?

• setup B : 0.664 mol Co

• setup A: 2.41x10⁴⁷mol Co

• setup A : 0.664 mol Co

• setup B: 2.41x10⁴⁷mol Co

Answer explanation

To convert atoms to moles, use Avogadro's number (6.022x10^23 atoms/mol). 4.00x10^23 atoms Co ÷ 6.022x10^23 atoms/mol = 0.664 mol Co. Thus, setup A: 0.664 mol Co is correct.

How many moles are in 98.3 grams of aluminum hydroxide, Al(OH)₃?

• 1.26 moles

• 0.8 moles

• 7,670 moles

• 1.63 x 10^-22 moles

Answer explanation

To find moles, use the formula: moles = mass (g) / molar mass (g/mol). The molar mass of Al(OH)3 is approximately 78 g/mol. Thus, 98.3 g / 78 g/mol = 1.26 moles, making the correct answer 1.26 moles.

To melt the ice, Stacy throws 455 g of calcium chloride, CaCl₂ on his sidewalk. How many moles of CaCl₂ did he throw?

• 50,500 moles

• 4.10 moles

• 7.56 x 10^-22 moles

• 111 moles

Answer explanation

To find moles of CaCl2, use the formula: moles = mass (g) / molar mass (g/mol). The molar mass of CaCl2 is 110.98 g/mol. Thus, 455 g / 110.98 g/mol = 4.10 moles. Therefore, the correct answer is 4.10 moles.