ch7 ef review answers

Ch7 ef review answers

Using this key, pick which category best describes the following chemicals: binary acid, oxy acid, covalent compound ( & not an acid), binary ionic compound (& not acid), or has a polyatomic ion( & not an acid). Then supply either the missing formula or name, & 2nd name for acids & covalent

oxy acid Carbonic acid or hyrdogen carbonate H₂CO₃

ionic… Magnesium sulfide MgS

polyatomic… Sodium carbonate Na₂ CO₃

binary acid.. Hl hydrogen iodide or hydroiodidic acid

ionic… CrO Chromium (II) oxide

polyatomic ion…. KOH potassium hydroxide

covalent…. Carbon IV oxide CO ₂

oxy acid…. H₂SO_{3 sulfurous acid hydrogen sulfite}

binary acid…. Hydrochloric acid HCl hydrogen chloride

covalent….. NO Nitrogen monoxide or Nitrogen (II) oxide

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Give the formulas; for acids and covalent compounds, give a 2nd name

potassium nitride K₃ N

nickel III nitride NiN

nitrite NO2^-1

hydrogen chlorate HClO₃ chloric acid

phosphorus trioxide PO₃ phosphorus (VI) oxide

nitrous acid hydrogen nitrite HNO ₂

nitrogen VI oxide NO₃ nitrogen trioxide

------------------------------------------------------------------------------------------------------------------------ find % sugar in gum from data. 3.00g before, 1.20g after chewing. 3-1.2= 1.8g of sugar;

1.8/ 3.00 = 60%

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salt water lab also on test! ch7 saltwater d&%

mass of dish 38.0g

mass of dish and 15mL of saltwater NaCl(aq) 59.0g

mass of dish and salt after oven 42.5g

mass of salt 4.5g

mass of water 16.5g

mas of saltwater 21g

density of salt water d=m/v= 21g/15mL = 1.4g/mL

% salt in salt water = salt/saltwater = 4.5/21= 21.4%

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A hydrate, barium sulfide triihydrate, is heated, and the following data is obtained.

BaS*3H2O

169 54 total 223

Mass of empty dish 34.06g

Mass of dish and hydrate 37.08g.

Mass of dish and chemical after heating 36.85g.

Mass in g of the hydrate 3.02g

Mass in g of the anhydrous salt 2.79g

Mass in g of the water .23g

% water in the hydrate from the experiment WORK: water/hydrate = .23/ 3.02 = 7.6%

% water in the hydrate from the formula WORK: water/hydrate = 54/223 = 24%

% error WORK: e-a/a = 7.6-24/24 = -68%

moles of water in the hydrate (from data) .23g/18 = .013 mole

moles of anhydrous salt 2.79g / 169 = .0165mole

no, this is about 1:1, we were expecting 3:1

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formula mass of CH_{4 = 12+1+1+1+1 =16 amu}

Common name and important uses (in our lab and in your home) of CH_{4 methane ; used for bunsen burners; heating the home and water.}

Formula mass of Sodium sulfate in amu Na₂S0₄ = 142

% S in Sodium sulfate WORK: 32/142 = 22.5%

% O in Sodium sulfateWORK: 64/142 = 45.1%

% Na in Sodium sulfate WORK: 46/142 = 32.4%

How many moles are 88g of carbon dioxide? WORK: 88/44 =2

What is the mass in grams of 0.55 moles of carbon monoxide? WORK: .55 mole * 28 = 15.4g

mass of 1 mole of sulfur VI oxide in g . SO3= 80g

moles of water present in 162g of water WORK: 162/18 = 9mole

mass of 0.61 mole of water in g WORK: .61mole *18 = 10.98g

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glucose and C2H6 are not empirical; glucose e.f. is CH2O, and C2H6 ef would be CH3

A sample of a compound decomposes into 92.3gC and 15.4gH ; it has a molar mass of 42g.

How many moles of H is 15.4g? WORK: 15.4/1=15.4 moles H

How many moles of carbon is 92.3g? WORK: 92.3/12= 7.7moles C

What is the mole ratio of H to C? WORK:

15.4mole H / 7.7mole C =2/1

What is the empirical formula?CH₂

What is the molecular to empirical formula ratio? WORK: 42/14=3/1

What is the molecular formula? 3(CH₂) = C₃H₆

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for more practice: p 253 (e242) #36-39 & p249 empirical and molecular formula problems; see sample problems in the text

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a chemist does not know the formula of a hydrate of sodium sulfate, so he heats the hydrate, obtaining the following data;

empty dish 32.50g

dish and hydrate 35.63g

dish and anhydrous salt 33.83

based on this information, what is the formula of the hydrate? Show work to justify your answer!

Na₂SO₄= 33.83-32.5=1.33g /142=.00937mole a.s.

H2O = 35.63-33.83 = 1.80g/18 = 0.10mole water

.10mole water/.00937mole a.s. = 10.7 round to 11

therefore Na₂SO₄ * 11H₂O

mg part below, skip for dec 2021

Why does magnesium gain mass when it burns, but wood loses mass when it burns? Oxygen stays with Mg (MgO) and Oxygen leaves in CO2 gas What is rust? iron (III) oxide Would an object appear to gain or lose mass as it rusts?

gain, oxide stays as solid

Some potassium metal is put into a crucible and heated, forming potassium oxide. The following data is collected.

Empty crucible 12.50g

Crucible and metal 14.45g

Crucible and product 15.25g

Assume the reaction is just like the magnesium reaction we did. Write a balanced chemical equation with states:

4K(s) + O₂(g) => 2 K₂O(s)

2 Mg(s) + O₂(g) = 2 MgO(s)

Mass of oxygen in grams = .8g

Mass of metal in grams = 1.95g

Mass of product in grams =2.75g

exp % oxygen in potassium oxide oxygen/potassium oxide = .8/2.75g = 29%

actual % oxygen in potassium oxide (from formula) oxygen/potassium oxide = 16/94 = 17%

% error = e-a/a = 29-17/17 = 70.5%

Moles of oxygen (from data)WORK: .8/16=.05 mole

Moles of metal (from data)WORK: 1.95/39 = .05 mole