Chemistry Basics & Measurements
Which of the following is a chemical change?
a. melting ice
b. boiling water
c. baking a cake
d. mixing baking soda and vinegar
c. baking a cake
Which element has 17 protons?
Chlorine (Cl)
Which of the following is an ionic compound?
a. H₂O
b. CO
c. NaCl
d. NH3
c. NaCl
How many moles are in 90.0 g of H₂O (molar mass = 18.0 g/mol)?
5.00 mol
In 2H₂O₂ → 2H₂O + O₂, how many moles of O₂ are produced from 4.00 mol H₂O₂?
2.00 mol O₂
How many significant figures are in 0.0023050?
5 significant figures
A neutral atom of ³¹P has how many neutrons?
16 neutrons
Write the formula for the compound formed between magnesium (Mg) and oxygen (O).
MgO
How many oxygen atoms are in 2.00 moles of SO₂?
2.41×1024 atoms.
In N₂ + 3H₂ → 2NH₃, which is the limiting reactant if 2.0 mol N₂ reacts with 4.0 mol H₂?
H₂ is limiting
Convert 7.50 km into m.
7.50 × 10³ m
The ion Ca²⁺ has how many electrons?
18 electrons
Name the compound PCl₅
Phosphorus pentachloride
Balance: Al + O₂ → Al₂O₃.
What is the coefficient in front of O₂?
3 (balanced: 4Al + 3O₂ → 2Al₂O₃)
In 2K + Cl₂ → 2KCl, if you start with 10.0 g K (molar mass = 39.1 g/mol) and 10.0 g Cl₂ (molar mass = 70.9 g/mol), which reactant is limiting?
K is limiting
A student measures 15.6, 15.7, and 15.8 mL when the actual value is 20.0 mL. Do the results show accuracy, precision, both, or neither?
Only precision.
Element Z has two isotopes: 10.0 amu (20%) and 11.0 amu (80%). What is its average atomic mass?
10.8 amu
Give the formula for iron(III) sulfate
Fe₂(SO₄)₃
A reaction has a theoretical yield of 42.0 g. If the actual yield is 36.0 g, what is the percent yield?
85.7%
In the reaction C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, how many grams of CO₂ are produced when 44.0 g of C₃H₈ reacts with excess O₂?
132 g CO₂
A metal has a density of 7.85 g/cm³. Express this density in kg/m³.
7.85×103 kg/m3
Which isotope of carbon is the most abundant and commonly found in nature?
a. 11C
b. ¹²C
c. ¹³C
d. ¹⁴C
b. ¹²C
A compound contains 52.0% C, 13.0% H, and 35.0% O by mass. What is its empirical formula?
C₂H₆O
In the reaction 2KClO₃ → 2KCl + 3O₂, how many grams of O₂ are produced from 245 g of KClO₃ (molar mass = 122.55 g/mol)?
96.0 g O₂
A mixture of 8.00 g H₂ (molar mass = 2.02 g/mol) and 64.0 g O₂ (molar mass = 32.0 g/mol) reacts via 2H₂ + O₂ → 2H₂O. Find the grams of H₂O formed.
Produces 72.0 g H₂O (H₂ is limiting)