Name______Date______Period______
Ch 1 & 2
These 3 questions refer to Substance Q, for which the solubility of Q is 99.2g/100 g water at 50.0°C.
1. How many grams of water are needed to dissolve 43.7 g of Q at this temperature? [ANS = 44.1 g]
2. The solution in (3), above, is cooled to 20.0°C, where the solubility of Q is 75.5 g Q/100 g water. How much Q crystallizes out of solution? [ANS = 10.4 g crystallizes since 33.3 g can dissolve @ 20°C]
3. A homogenous solution of substance Q is made from 29.0 g of Q and 35.0 g water at 50°C. The solution is (unsaturated, saturated, supersaturated)? [ANS = unsaturated since 34.7 g Q could dissolve in 35.0 g H2O at 50°C]
When the temperature drops 12.2 degrees Centigrade (Celsius) what is the final temperature (in degrees Fahrenheit) if the starting temperature was 14.3 degrees Fahrenheit? [ANS = -7.65°F, go into °C then subtract 12.2°C then go back to °F]
The circumference of the earth is about 2.50 x 104 miles. What is the approximate radius of the earth in kilometers based on the information provided? (1 mile = 1.609 km) [4.02 x 104 km]
A student was asked to find the density of an unknown liquid. The following measurements were made in a laboratory at 20oC. The student saw 71.000g on the balance when weighing the flask and stopper empty, but wrote down 71 g rather than recording all of the zeroes.
Mass of empty flask plus stopper: 71 g
Mass of stoppered flask plus liquid: 128.125 g
Volume of “calibrated” flask: 63.021 mL
Be sure to use the correct number of “significant figures” according to the student’s results.
1. Calculate the density of the liquid using the data in the box above. [ANS = 0.91 g/ml]
2. What is the density of the unknown liquid when using the more precise value of 71.000 g for the first measurement? [ANS = 0.90644 g/ml]
Suppose a student has copper (II) nitrate and Fe(NO3)3 in her unknown sample in the Paper Chromatography lab in this course. She identifies them using her known solutions, and calculates the Rf values for each metal ion. The solvent moves 7.2 cm during the experiment. The Rf value for the copper (II) nitrate is 0.46.
1. What is the formula for copper (II) nitrate?
2. What is the name for Fe(NO3)3 ?
3. The Fe ion traveled 5.3 cm up the paper during the experiment. What was its Rf value?
4. How far did the copper ion travel up the paper during the experiment?
5. If the experiment had been carried out twice as long, with taller filter paper, which of the following would be true?
(a) Both Rf values would increase and the ions would be further apart at the end.
(b) Both Rf values would decrease and the ions would be closer together at the end.
(c) The ions would be further separated because the larger Rf value would get bigger and the smaller Rf value would get smaller.
(d) The Rf values would remain constant and the ions would be further apart.
(e) The Rf values would remain constant and the ions would be closer together.
[ANS = Cu(NO3)2, iron(III) nitrate, 0.74, 3.3 cm, d]
The solubility of Li2SO4 is 31 g/100 g H2O at 80ºC and 35 g/100 g at 20ºC. The solubility of KCl is 67 g/100 g H2O at 80ºC and 32 g/100 g at 20ºC. Water at 80ºC is saturated with both at 80ºC and then cooled to 20ºC. Which precipitates? [ANS = KCl]
Consider the following lab data used to find the density of an unknown solid sample
Density Methanol = 0.791 g/ml
Mass Flask + Stopper = 107.25 g
Mass Flask + Stopper + Methanol = 154.47 g
Mass Flask + Stopper + Solid = 132.42 g
Mass Flask + Stopper + Solid+ Methanol = 176.12 g
a) What is the volume of the flask?
b) What is the density of the solid? [ANS = 59.7 ml, 5.6 g/ml]
How many grams of water are required to dissolve a mixture made from 18 g of A (solubility = 14 g A/100 g water) and 23 g of B (solubility = 25 g B/100 g water), assuming the solubilities are independent of each other? [ANS = 128.6 g water]
What is the density of a liquid which, when measured in a flask that holds 50.00 mL, weighs 43.225 g? [ANS = 0.8645 g/ml]
Calculate the density (g/cm3) of a plastic cube that is 5.00 cm on a side and has a mass of 203.75 g. [ANS = 1.63 g/cm3]
A saturated solution of compound Q is produced by dissolving 17.5 g of Q in 50.0 g of water. What is the solubility of Q in grams Q per 100.0 g of water? [ANS = 35.0 g]
The density of a certain vegetable oil is 0.855 g/cm3. When placed in a beaker with water, which (water or oil) will settle to the bottom of the beaker? [ANS = water]
What is the value of absolute zero (-273.15°C) in Fahrenheit? [ANS = -459.67°F]
Calculate (2.36 – 0.899)*5.445 to the proper number of sig fig’s. [ANS = 7.96]
Compound A has a solubility of 22.0g/100g water at 27°C and 45.0g/100g at 75°C.
1. How much water is needed to dissolve 48.0 g of the compound at 27°C?
2. A 35.0 g sample of A is added to 85.0 g of water at 75°C. The solution is then cooled to 27°C. How many grams of A will crystallize out?
[ANS = 218 g H2O, 16.3 g A]
The number of significant figures in the answer to (51.5 – 2.67) x (33.42 – 0.124) is
[ANS = 3 , 1.63 x 103]
Which of the following has the largest volume? 1 cup = 225 mL [ANS = D]
A) 2/3 cup B) 150 mL C) 3.78 x 10-2 cup D) 0.75 cup
An infant ibuprofen suspension contains 100mg/5.0 mL suspension. The recommended dose 10 mg/kg body weight. How many mL of this suspension should
be given to an infant weighing 18 lb? (Assume 2 significant figures). 1 lb = 453.6 g
[ANS = 4.1 ml]
A student made the measurements below in order to obtain the density of an unknown solid. In the experiment, the volume of the flask was determined by finding the mass of ethanol required to completely fill the empty flask.
Mass of flask + stopper = 29.245 g
Mass of flask + stopper + ethanol = 48.639 g
Density of ethanol = 0.789 g/mL
Mass of flask + stopper + solid = 54.623 g
Mass of flask + stopper + solid + ethanol = 71.776 g
1. What is the volume of the flask?
2. What is the mass of the unknown?
3. What is the volume of the unknown?
4. What is the density of the unknown?
[ANS = 24.6 ml, 25.378 g, 2.9 ml, 8.8 g/ml]
An empty flask weighs 65.228 g. The flask is completely filled with water, and the mass of the flask and water is measured at 98.002 g. If the density of water is 0.9987 g/mL, calculate the volume of the flask. [ANS = 32.82 ml]
Solute A has a solubility of 22 g/100 g H2O. How many grams of A should be added to 78 g of water to make a saturated solution? [ANS = 17.2 g A]
How many 81 mg tablets can be made from 1.21 kg aspirin? [ANS = 14,938 tablets]
A plastic block is 2.2 cm x 3.0 cm x 1.5 cm and has a mass of 12.4 grams. Will the block float in water and why? (density of water = 1.00 g/mL) [ANS = c]
a) No, the density of block is 0.80 g/mL which is greater than the density of water.
b) Yes, the density of the block is 1.3 g/mL which less than the density of water.
c) No, the density of block is 1.3 g/mL which is greater than the density of water.
d) Yes, the density of the block is 0.80 g/mL which is less than the density of water.
e) none of the above
The solubility of sucrose at 20°C is 204 g/100 g of water and at 100°C is 487g/100 g. A solution at 100°C is prepared by dissolving 245 g of sucrose in 77.0 g of water. The solution is cooled to 20°C. How many grams of sugar crystallizes? [88 g]
A student made the measurements below in order to obtain the density of an unknown solid. In the experiment, the volume of the flask is determined by finding the mass of mercury (a dense liquid) required to completely fill the empty flask.
Mass of flask + stopper = 49.5770 g
Mass of flask + stopper + mercury = 182.2263 g
Density of mercury = 13.5939 g/mL
Mass of flask + stopper + solid = 131.2896 g
Mass of flask + stopper + solid + mercury = 205.1045 g
1. What is the volume of the flask?
2. What is the mass of unknown solid?
3. What is the volume of the unknown solid?
4. What is the density of the unknown solid?
[ANS = 9.75800 ml, 81.7126 g, 4.32800 ml, 18.8800 g/ml]
A solution is 12.0% of sodium hydroxide by mass and has a density of 1.131 g/mL. What volume of this solution (in mL) contains 3.50 g of sodium hydroxide?
Ch 3
A solution is made of 0.50 mol table salt (NaCl) and 0.50 mol water. What is the mass percent water in the solution? [ANS = 23.6%]
What is the mass percent oxygen in (NH4)2CO3 •10H2O? [ANS = 75.4%]
What is the simplest formula of a compound containing only hydrogen and nitrogen, which is 12.6% hydrogen by mass? If the substance has a real molar mass of 32 g/mol, what is its molecular formula? [ANS = Simplest is NH2, molecular is N2H4]
For a given reaction, the actual yield is 63.0 g. If this represents 66.0% of the theoretical yield, what is the theoretical yield? [ANS = 95.5 g]
Suppose that, instead of carbon-12, fluorine-19 had been chosen as the basis for atomic masses. If it were assigned a mass of exactly 10.000, what would the atomic mass of iron be? [ANS = 29.4 g/mol]
If the molar mass of a compound is 180.16 g/mol, and its empirical formula is CH2O, what is its molecular formula? [ANS = C6H12O6]
How many H atoms in a cup (8 fluid ounces at 28.4mL/ounce) of CH3OH? Density = 0.7918 g/mL [ANS = 1.35 x 1025]
What is the mass of 18.3 moles H2SO4? [ANS = 1,794.8 g]
The density of ethanol, C2H5OH, is 0.789 g/mL. 45.6 mL of ethanol are burned to produce CO2 and water. How many grams of water are produced? [ANS = 42.2 g]
C2H5OH(l) + 3O2(g) à 2CO2(g) + 3H2O
Tartaric acid is the white, powdery substance that coats sour candies such as Sour Patch Kids. It contains the elements H, C, and O. Combustion analysis of a 12.01 g sample of tartaric acid produced 14.08 g CO2 and 4.32 H2O.
Calculate the number of mols and mass of H.
Calculate the number of mols and mass of C.
Calculate the number of mols and mass of O.
What is the simplest formula of "tartaric acid"?
[ANS = 0.48 g H, 0.48 mol H, 3.84 g C, 0.32 mol C, 7.69 g O, 0.48 mol O, C2H3O3]
Consider the following balanced equation. How many mols of SO2 needed to produce 165 grams of S?
2 H2S(g) + SO2(g) à 3 S(s) + 2 H2O(g)
One of the major components of beeswax has the formula C56H118O2 (MM=824 g/mol). Suppose a 1 lb (435g) candle made of that compound is lit and burns producing carbon dioxide and water. It is placed in a small, sealed room that contains 66 mols of oxygen in the air and left to burn. Does the candle burn completely or is the oxygen in the room consumed first?
1. Write a balanced chemical equation for the burning of the wax.
2. How many mols wax are in the candle?
3. How many mols oxygen are required to completely burn the candle?
4. Is wax or oxygen left over and how many mols of it remain?
Consider the reaction between Si and nitrogen for the formation of Si3N4(s).
3Si(s) + 2N2(g) à Si3N4(s)
15 grams of Si and 25 grams of nitrogen are reacted to form Si3N4(s).
1. If 15 g of Si reacts with excess N2 , how many moles of Si3N4 are produced?
2. If 25 g of N2 reacts with excess Si, how many moles of Si3N4 are produced?
3. If 15 g of Si and 25 g of N2 are reacted, how many moles of Si3N4 can be formed if the percentage yield is 85%? [ANS = 0.178 moles, 0.446 moles, 0.151 moles]
Consider potassium chlorate KClO3 (MM = 122.6 g/mol).
1. How many oxygen atoms are there in 5.43 grams of potassium chlorate?
2. How many grams of potassium are there in 3.45 grams of potassium chlorate?
Suppose fluorine were used as the basis of atomic mass, and assigned a mass of 9.00. What would the atomic mass of copper be when using this basis?
What is the simplest formula for the compound C6H12O6?
Consider the unbalanced reaction:
__CH3NH2(g) + __O2(g) → __N2(g) + __H2O(g) + __CO2(g)
Once balanced, what is the sum of coefficients for the products (use
smallest whole number coefficients)? [16, balanced rxn coefficients are 4,9,2,10,4]]
If the actual yield of a reaction is 68.2 % and 15.5 g of product forms, what is the theoretical yield? [22.7 g]
The compound C6H12O2N has half as many grams of carbon as hydrogen (Y or N)? [No, has 72 g C and 12 g H, it has half as many moles of C as H]
What is the mass, in grams, of 6.52 x 1021 molecules of aspirin, C9H8O4? [1.95 g]
What is the mass percent of O in a compound with a formula C7H5(NO2)3
(MM = 227.14 g/mol)?
Lead (II) oxide reacts with ammonia as follows:
3PbO(s) + 2NH3(g) à 3Pb(s) + N2(g) + 3H2O(l)
1. How many grams of PbO are consumed in the reaction of 8.16 g PbO?
(MM of PbO is 223.2 g/mol)
2. If 0.312 g of NH3 is available to react with 8.16 g PbO, how many grams of
Pb are produced?
3. If the actual yield is 4.95 g Pb, what is the percent yield?
[ANS = 0.415 g, 5.69 g, 87%]
Benzocaine is a compound containing carbon, oxygen, hydrogen and
nitrogen. When a sample of benzocaine weighing 3.54 g is burned in excess
oxygen, 8.49 g of CO2 and 2.14 g of H2O are formed. In a separate experiment, the
percentage of N is determined to be 8.468 %.
1. How many grams of carbon are in the sample?
2. How many grams of hydrogen are in the sample?
3. How many grams of nitrogen are in the sample?
4. How many grams of oxygen are in the sample?
5. What is the simplest formula?
[2.32 g C, 0.239 g H, 0.300 g N, 0.681 g Ox, C9H11O2N)