Matter & Atoms
Classify distilled water:
element, compound, or mixture?
compound
Name Na2SO4.
Sodium Sulfate
Balance: Mg + O2 → MgO.
2Mg+O2→ 2MgO
What is a precipitate?
An insoluble solid formed in a solution reaction.
Define molarity and its unit
M = mol solute / L solution
mol/L.
A reaction releases heat. Exothermic or endothermic?
Exothermic
ΔH is negative
How many protons, neutrons and electrons are in sodium(Na)-23?
11 protons, 12 neutrons, 11 electrons.
Write the formula of calcium nitrate.
Ca(NO3)2
Classify: 2KClO3 → 2KCl + 3O2.
Decomposition reaction
Which is a strong electrolyte and why?
NaCl(aq) or Glucose(aq)
NaCl
it dissociates into ions.
Calculate molarity:
0.50 mol NaCl in 2.00 L solution
0.250 M
What does ΔH = +85 kJ mean?
Endothermic- absorbs 85 kJ at constant pressure
A measurement is close to the accepted value but repeated measurements vary widely. Is it accurate or precise?
accurate
Name FeCl3 and N2O5.
Iron(III) chloride
Dinitrogen pentoxide
How many moles are in 18.0 g H2O?
Approximately 1.00 mol (molar mass 18.02 g/mol).
What precipitate forms when AgNO3(aq) and NaCl(aq) mix?
name the compound
AgCl(s)
Silver chloride.
Calculate molarity of 4.00 g NaOH in 250.0 mL.
Molar mass 40.00 g/mol
0.400 M
Calculate q for 100 g water heated from 20°C to 30°C. c = 4.184 J/(g·°C).
+4184 J = +4.184 kJ
How many protons, neutrons and electrons are in iron-56, Fe3+?
26 protons, 30 neutrons, 23 electrons.
Write formulas for ammonium phosphate and aluminum oxide
(NH4)3PO4 and Al2O3
Balance and classify
C3H8 + O2 → CO2 + H2O.
C3H8 + 5O2 → 3CO2 + 4H2O.
Combustion
Write net ionic equation for HCl(aq) + NaOH(aq).
H+ (aq) + OH− (aq) → H2O(l).
Volume of 2.00 M HCl needed for 250.0 mL of 0.200 M HCl?
25.0 mL using M1V1 = M2V2
Reaction releases 500 J heat; 200 J work done ON system. Find ΔU.
ΔU=q + w = −500 + 200 J=−300 J.
Chlorine has 75% chlorine-35 and 25% chlorine-37. Calculate average atomic mass.
(0.75 × 35) + (0.25 × 37)= 35.5 u
Empirical formula CH2O; molar mass 180 g/mol.
Find molecular formula.
C6H12O6.
2Mg + O2 → 2MgO
How many grams MgO from 12.0 g Mg and excess O2?
(12.0 / 24.31) × 40.31
19.9 g MgO.
Write net ionic equation for BaCl2(aq) + Na2SO4(aq).
Ba2+ (aq) + SO4 2− (aq) → BaSO4(s).
How many grams NaCl for 500.0 mL of 0.300 M solution? Molar mass 58.44 g/mol.
8.77 g NaCl
In peroxide decomposition, concentration changes; time until bubbling stops is measured. Identify variables
Independent: concentration.
Dependent: time until bubbling stops
A compound contains 40.0% C, 6.7% H and 53.3% O by mass. Find its empirical formula.
CH2O. In 100 g: C ≈ 3.33 mol, H ≈ 6.65 mol, O ≈ 3.33 mol; ratio 1:2:1.
Name Cu(NO3)2 and PCl5.
Why do naming systems differ?
Copper(II) nitrate and phosphorus pentachloride.
Ionic naming uses a Roman numeral; molecular naming uses prefixes.
N2 + 3H2 → 2NH3
Given 2.0 mol N2 and 3.0 mol H2, identify limiting reactant and NH3 formed
H2 is limiting
2.0 mol NH3 forms.
For Zn + CuSO4 → ZnSO4 + Cu,
identify oxidation, reduction and oxidizing agent.
Zn oxidized to Zn2+; Cu2+ reduced to Cu
Cu2+ is oxidizing agent.
Mix 25.0 mL 0.200 M BaCl2 with 30.0 mL 0.100 M Na2SO4. Grams BaSO4 formed? Molar mass 233.39 g/mol
0.700 g BaSO4.
Sulfate limits: 0.00300 mol × 233.39 g/mol
5.0 g sugar dissolves in 100 mL water at 20, 40, 60°C in 130, 85, 48 s. Identify variables, two controls and trend
Independent: temperature
dependent: dissolution time.
Controls: sugar mass, water volume. Higher temperature correlates with shorter time