1.Perform the Following Conversions

Fall 2015

Chem 1A, Test Review #1

1.Perform the following conversions:

(a) 1.60 yard to centimeters (cm); (1 yard = 36 inches (exactly); 1 inch = 2.54 cm (exactly))

(b) 25 miles per gallon (mpg) to km per liter (kmpL);

(1 mile = 1.609 km; 1 gallon = 3.7854 L)

(d) 115oF to degrees Celsius (oC) and to Kelvin, respectively.

(e) The masses of four different samples of sodium chloride were measures as follows:

22.5 g, 5.238 g, 5,182 mg, and 723.5 mg. What is the total mass of salt with correct significant figures?

2.Indicate whether each of the following is a physical or chemical process:

(a) Silver tarnishes;(e) alcohol vaporizes;

(b) Butter turns rancid;(f) the lake is frozen;

(d) The toast is burnt;(h) The sugar has re-crystallized.

3.Classify each of the following as an element, a compound, a homogeneous or heterogeneous mixture:

(a) A bag of jelly beans;(e) A gallon of methanol;

(b) A cup of pure cane sugar; (f) A tank of gasoline;

(d) A glass of white wine;(h) A sac of saw dust.

4.A cylindrical metal bar thatis 5.50 cm long weighs 19.70 g. The bar displaces 7.3 mL of water when completely submerged. Calculate the density the metal and the diameter of the bar?

5.Complete the following table for isotopes of elements.

Name of Element / Atomic Number / Mass Number / Number of Protons / Number of Neutrons / Number of Electrons / Isotope Symbol
Magnesium / 13 / 10
15 / 16 / 15
Cu
108 / 47 / 46
Pb2+

6.Tungsten exists in two naturally occurring isotopes with the following atomic masses and natural abundance: 185W (184.953 u; 37.07%) and 187W (186.956 u; 62.93%). Calculate the weighted average atomic mass of tungsten.

7.An element E reacts with oxygen gas to form an oxide with the formula E2O3. If the mass percent of oxygen in the oxide is 17.29%, calculate the atomic mass of E and identify the element.

8.Name each of the following compounds:

(a) NH4NO3 : ______;(g) PCl5:______

(b) Na2CO3: ______;(h) HBrO2:______

(d) K2HPO4:______;(j) K2Cr2O7 :______

(e) NiSO4:______;(k) SF6 :______

(f) CrCl36H2O: ______;(l) HIO4 :______

9.Write the correct formula of each of the following compounds:

(a) Calcium hypochlorite: ______;(g) Ammonium sulfate:______

(b) Sodium phosphate: ______;(h) Hydrosulfuric acid:______

(d) Lead(II) acetate:______;(j) Diboron trioxide:______

(e) Carbon tetrachloride: ______;(k) Potassium permanganate: ______

(f) Lithium carbonate: ______;(l) Barium hydroxide: ______

10.(a) A compound composed of 68.85% carbon, 4.95% hydrogen, and 26.20% oxygen, by mass, has a molecular mass of 122 amu. determine the empirical formula and the molecular formula of the compound.

(b) When a 2.451-g sample of a compound that is composed of carbon, hydrogen and oxygen, is completely combusted, it produces 5.821 g of CO2 and 2.979 g of H2O. Determine the mass percent composition of the compound. Calculate the empirical formula of the compound.

11.Write a balanced equation for each reaction described below:

(a) Solid ammonium dichromate decomposes when heated to produce solid chromium(III) oxide, nitrogen gas, and water vapor.

(b) Calcium metal reacts with water to produce aqueous calcium hydroxide and hydrogen gas.

12.Balance the following chemical equationsusing the smallest integer coefficients.

(a) ___C4H10O(l) + ___O2(g)  ___CO2(g) + ___H2O(g);

(b) ___NH3(g) + ___O2(g)  ___NO(g) + ___H2O(g);

13.The following equation represents the combustion of octane (C8H18):

2C8H18(l) + 25 O2(g)  16CO2(g) + 18H2O(g)

(a) How many grams of O2 gas are consumed during the combustion of 345 g of octane?

(b) How many grams of CO2 and H2O, respectively, are produced when 345 g of octane is completely combusted?

14.An ammonium phosphate fertilizer is prepared by the following reaction:

3NH3(g) + H3PO4(aq)  (NH4)3PO4(s)

(a) If a reaction uses 245 g H3PO4 and 115 g NH3, which is the limiting reagent?

(b) How many grams of ammonium phosphate, (NH4)3PO4, will be produced when the limiting reactant is completely reacted and the reaction yield is 100%?

(d) If 318 g of ammonium phosphate were produced, what is the percent yield?

(e) How many grams of theexcess reactant will remain unreacted at the end of the reaction?

15.Magnesium hydroxide, Mg(OH)2, decomposes when heated to form magnesium oxide and water vapor according the following equation:

Mg(OH)2(s)  MgO(s) + H2O(g)

When a 5.00-g solid mixture that contains Mg(OH)2and MgO is heated untilall of the Mg(OH)2in the mixture is completely decomposed,the solidresidue that remains is found to weigh 3.65 g.

(a) Calculate the mass and the number of moles of water vapor given off. (b) How many grams of Mg(OH)2was present in the original mixture? (c) Calculate the mass percent of Mg(OH)2 in the mixture.

Answers:

1.(a) 146 cm(b) 11 KmpL (c) 65.8 kg (d) 46.1oC; 319.3K (e) 33.6 g

2.(a) Chemical change(b) Chemical (c) Physical change(d) Chemical

(e) Physical(f) Physical (g) Chemical (h) Physical

3.(a) Heterogeneous mixture(b) Compound(c) Heterogeneous mixture

(d) Homogeneous mixture(e) Compound(f) Homogeneous mixture

(g) Element(h) Heterogeneous mixture

4.Density = 2.70 g/mL;diameter = 1.30 cm

5.ElementAtomic No.Mass No.# Protons# Neutrons# ElectronsIsotope

Magnesium122512131025Mg2+

Phosphorus153115161531P

Copper296329342963Cu

Silver47108476146108Ag+

Lead822078212580207Pb2+

6.Weighted average atomic mass of Tungsten = 186.21 amu

7.Atomic mass of element E = 114.8 amu = Sb

8.(a) Ammonium nitrate(b) Sodium carbonate(c) Silicon tetrafluoride

(d) Potassium hydrogen phosphate(e) Nickel(II) sulfate(f) Chromium(III) chloride

Hexahydrate

(g) Phosphorus pentachloride(h) Bromous acid(i) Iron(III) hydroxide

(j) Potassium dichromate(k) Sulfur hexafluoride(l) Periodic acid

9.(a) Ca(OCl)2(b) Na3PO4(c) H3PO4(d) Pb(C2H3O2)2(e) CCl4(f) Li2CO3

(g) (NH4)2SO4(h) H2S(i) CuSO4.5H2O(j) B2O3(k) KMnO4(l) Ba(OH)2

10.(a) Empirical formula = C7H6O2 = Molecular formula

(b) 64.83% C; 13.60% H and 21.57% O; empirical formula = C4H10O

11.(a) (NH4)2Cr2O7(s)  Cr2O3(s) + N2(g) + 4H2O(g)

(b) Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)

12.(a) C4H10O(l) + 6 O2(g)  4CO2(g) + 5H2O(g)

(b) 4NH3(g) + 5 O2(g)  4NO(g) + 6H2O(g)

13.(a) Mass or O2 consumed = 1.21 x 103 g

(b) Mass of CO2 produced = 1.06 x 103 g;Mass of H2O produced = 490. G

14.(a) Mole of H3PO4 = 2.50 moles; mole of NH3 = 6.75 moles; NH3 is the limiting reactant;

(b) Mass of (NH4)3PO4 = 336 g (at 100% yield);(c) = 307 g (at 91.5% yield;

(d) % yield = 94.6%;(e) Mass of H3PO4 unreacted = 24.4 g

15.(a) Mass of H2O = 1.35 g; mole of H2O = 0.0749 mole;

(b) Mass of Mg(OH)2 in mixture = 4.37 g; % of Mg(OH)2 in mixture = 87.4%