Quantitative Chemistry

Moles

100

True or false: 1 mole of water (H₂O) contains more molecules than 1 mole of phenol (C₆H₆O).

False: mole is like a dozen, and 1 dozen is 1 dozen is 1 dozen!

200

What is the molar mass of HBr?

80.91 g/mol.

300

The chemical formula for guanine is C5H5N5O

Its molar mass is...?

151.13 g/mol

400

How many hydrogen *atoms* are in 10.0 moles of ethanol, C₂H₅OH?

1 mole ethanol => 6 moles H

10 moles => 60 moles H

60*L => 3.612 x 10²⁵

500

5 umol (micromole) of a immunoprotein (M = 150,000) weighs ___?

0.150 x 5 = 0.750g.

Formulae

100

True or false: C₄H₁₀ is an empirical formula.

False: the simplest ratio between the elements is 2:5, and the empirical formula is thus C₂H₅.

200

Write the empirical formula for ozone (O₃).

O.

300

What is the total number of ions in Al₂(SO₄)₃?

2+3 = 5

400

Which of the following compounds has/have the empirical formula CH₂O?

 _{I: CH3COOH
 II: C6H12O6
 III: C12H22O11}

I & II

500

Pyrite (fool's gold) has an empirical formula of FeS₂. What is its %Fe by mass?

32+32+55.8 = 119.8

55.8 / 119.8 = 46.5%

Equations

100

True or false: If we sum up the coefficients on the LHS of a equation, it will always matches the sum of coefficients on the RHS.

False: the species can contain different distribution of elements!

200

Ethanol dissolves in contact with water. Write an equation that describes this transformation.

C₂H₅OH_(l) -> C₂H₅OH_(aq)

300

Write and balance the equation:

Potassium reacts with water to give potassium hydroxide and hydrogen gas.

2K_(s) + 2H₂O_(l) -> 2KOH_(aq) + H_2(g)

400

NH₃ + HF --> NH₃.HF

34g NH3 and 34g of HF

What is the limiting reagent?

2 moles; 1.7 moles. HF is limiting.

500

CaCO3 -> CaO + CO2

50g CaCO3 reacted to give 7g of CaO

%yield = ?

0.5 mole theoretical yield,

0.5 x 56 = 28

25%

Gases

100

True or false: gases can directly transform into either solids or liquids.

True: reverse sublimination and condensation.

200

What temperature does "STP" refer to?

0 celsius / 273 K.

300

Give one condition when the ideal gas law fails.

Very low temperature, or very high pressure. Both diminishes the large distance otherwise present in gases.

400

HF (hydrogen fluoride) has a molar mass of 20.0 g/mol. 10.0 g of HF occupies a volume of ____ at STP.

0.5 mol -> 11.2 dm³

500

Ca_(s) + 2H₂O_(l) -> Ca(OH)_2(aq) + H_2(g)

What is the volume of gas, at STP, produced when 0.400 g of Ca_(s) reacts completely with water?

Molar mass = 40 g/mol 0.400/40 = 0.0100 moles = 0.0100 moles => 22400 mL x 0.0100 = 224mL