Concept #1:

**Mass** or **weight percent** is the percentage of a given element or compound within a solution.

Example #1:
Calculate the amount of water (in kilograms) that must be added to 12.0 g of urea, (NH_{2})_{2}CO, in the preparation of a 18.3 percent by mass solution. The molar mass of urea, (NH_{2})_{2}CO, is 60.055 g/mol.

Example #2:

A solution was prepared by dissolving 51.0 g of KBr in 310 mL of water. Calculate the mass percent of KBr in the solution.

Practice: At 298 K, a solution is prepared by dissolving 12.7 g NaCl in 95.5 mL of water. What is the ppm of NaCl if the density of water at this temperature is 0.9983 g/mL.

Determine the percent sulfuric acid by mass of a 1.37 m aqueous solution of H 2SO4.A) 0.1342%B) 11.84%C) 13.42%D) 13.98%E) 1.37%

The chemist must prepare 1.00 kg of 15.0% (w/w) acetic acid using a stock solution which is 36.0% (w/w) acetic acid (d = 1.045 g/mL). Which of the following combinations will give her the solution she wants?A) 417 mL of 36% acetic acid in 583 mL of distilled waterB) 417 g of 36% acetic acid in 583 g of distilled waterC) 360 mL of 36% acetic acid in 640 mL of distilled waterD) 360 mL of 36% acetic acid in 640 g of distilled waterE) 150 g of 36% acetic acid in 850 g of distilled water

What is the percent CdSO4 by mass in a 1.0 molal aqueous CdSO4 solution?A. 0.10 %B. 20.8 %C. 17.2 %D. 24.4 %E. 0.001%

A stock solution of hydrofluoric acid is 15 M and has a density of 0.99 g/mL at 25 °C. What is the mass percent of HF at 25 °C?a. 15%b. 30%c. 45%d. 60%

A solution was prepared by dissolving 39.0 g of KCl in 225 mL of water. Calculate the mass percent of KCl in the solution.

How many moles of each substance are needed to prepare the following solutions? Part A 67.0 mL of 9.5% m/v KCI (MW 74.55 g/mol)Express your answer using two significant figures. Part B 350.0 mL of 90%m/v acetic acid (Mw 60.06 g/mol) Express your answer using two significant figures.

A 3.56 g sample of a laboratory solution contains 1.97 g of acid. What is the concentration of the solution as a mass percentage?

Part AA hydrocarbon is a compound that contains mostly carbon and hydrogen. Calculate the percent composition (by mass) of the following hydrocarbon: C10H22. Enter the percentages of carbon and hydrogen numerically to four significant figures separated by commas.

Hydrochloric acid is usually purchased in a concentrated from that is 37.0%. HCl by mass and has a density of 1.20 g/mL. Part A How much concentrated solution would you take to prepare 2.85 L of 0.420 M HCl by using with water?

How many grams of Al(NO3)3 are present in 58.9 g of a(n) 12.4% by mass Al(NO3)3 (aq) solution? Enter only a numerical answer. Do not include units.

Citric acid (right) is concentrated in citrus fruits and plays a central metabolic role in nearly every animal and plant cell. How many moles of citric acid are in 9.84 qt of lemon juice (d = 1.09 g/mL) that is 7.61% citric acid by mass?

For a plant food labeled 23-19-17, calculate: Your answer should be in two significant figures. a % nitrogen b. % phosphorus c. % potassium Calculate % sulfate (SO4) in CuSO4. Your answer should be in one significant figure.

A chemist mixes 87. g of acetone with 93. g of 1-bromobutane and 94. g of thiophene. Calculate the percent by mass of each component of this solution. Be sure each of your answer entries has the correct number of significant digits.

If a buffer solution is 0.270 M in a weak acid (Ka = 1.8 x 10-6) and 0.430 M in its conjugate base, what is the pH?

Isopropyl alcohol is mixed with water to produce a 31.0% (v/v) alcohol solution. How many milliliters of each component are present in 665 mL of this solution? (Assume that volumes are additive.)

Load is a basic metal that affects the central nervous system. A Pb-water sample contains 0.0011 % Pb by mass.How much of the water (in mL) contains 1.65 mg of Pb? (Assume a density of 1.0 g/mL) Express your answer using two significant figures.

How many grams of Na2CO3 are present in 12.4 mL of a solution that is 39.0% Na2CO3, by mass. The density of the solution is 1.19 g/mL.

You need to dissolve CaCl2 in water to make a mixture that is 36.5% calcium chloride by mass. If the total mass of the mixture is 180.7 g, what masses of CaCl2 and water should be used?

The amount of nitrogen in an organic substance can be determined by an analytical method called the Kjeldahl method, in which all the nitrogen in the organic substance is converted to ammonia. The ammonia, which is a weak base, can be neutralized with hydrochloric acid, as described by the equation NH3(aq) + HCl(aq) → NH4Cl(aq) If 47.0 mL of 0.150 M HCl(aq) is needed to neutralize all the NH3(g) from a 2.25-g sample of organic material, calculate the mass percentage of nitrogen in the sample.

Enter your answer in the provided box.Calculate the mass % of Br in barium perbromate.

Be sure to answer all parts.Calculate the amount of water (in grams) that must be added to each of the following substances to produce the indicated solution. (a) 5.30 g of urea (NH2)2CO in the preparation of a 20.9 percent by mass solution: (b) 34.5 g of MgCl2 in the preparation of a 3.2 percent mass solution:

A particular coal contains 2.55% sulfur by mass. When the coal is burned, it produces SO2 emissions which combine with rainwater to produce sulfuric acid.a. Use the formula of sulfuric acid to calculate the mass percent of S in sulfuric acid.b. Determine how much sulfturic acid (in metric tons) is produced by the combustion of 1.0 metric ton of this coal. (A metric ton is 1000 kg.)

Calculate the percent composition of the following compounds. Write all values to two decimal places.

A solution was prepared by dissolving 32 g of KCl in 225 g of waterCalculate the mass percent of KCl in the solution

You need to dissolve CaCl2 in water to make a mixture that is 35.5% calcium dichloride by mass. If the total mass of the mixture is 719.9 g, what masses of CaCl2 and water should be used?

Table salt, NaCl(s), and sugar, C12H22O11 (s), are accidentally mixed. A 5.50-g sample is burned, and 1.60 g of CO2 (g) is produced. What was the mass percentage of the table salt in the mixture?

An alloy contains 69 g of pure gold and 37 g of pure zinc. What is the percentage of zinc in the alloy? Express your answer to two significant figures and include the appropriate units.

A certain ore is 33.7% nickel by mass. How many kilograms of this ore would you need to dig up to have 60.0 g of nickel?

Be sure to answer all parts.Calculate the amount of water (in grams) that must be added to each of the following substances to produce the indicated solution. (a) 5.70 g of urea (NH2)2 CO in the preparation of a 24.8 percent by mass solution: (b) 33.1 g of MgCl2 in the preparation of a 4.9 percent mass solution:

What is the mass percentage of iodine (I2) in a solution containing 3.0 x 10-2 mol I in 140 g of CCL4? Express your answer using two significant figures.

You wish to prepare 210 grams of 16.2 % FeCl3. You will need ______ grams of iron(III) chloride and _______ mL of water. Assume that the density of water is 1.00 g/ml.

A 4.97 g sample of a laboratory solution contains 1.03 g of acid. What is the concentration of the solution as a mass percentage?

How many grams of NiF2, are there in 191 grams of an aqueous solution that is 6.65 % by weight NiF2.

A sample weighing 3.093 g is a mixture of Fe 2O3 (molar mass = 159.69) and Al 2O3 (molar mass = 101.96). When heat and a stream of H2 gas is applied to the sample, the Fe2O3 reacts to form metallic Fe and H2O(g). The Al2O3 does not react. If the sample residue (the solid species remaining after the reaction) weighs 2.313 g, what is the mass fraction of Fe2O3 in the original sample?

An alloy contains 59 g of pure silver and 20 g of pure copper. What is the percentage silver in the alloy? Express your answer to two significant figures and include the appropriate units.

A 7.91 g sample of an aqueous solution of hydrochloric acid contains an unknown amount of the acid. lf 10.6 mL of 1.55 M sodium hydroxide are required to neutralize the hydrochloric acid, what is the percent by mass of hydrochloric acid in the mixture?

A student is running an experiment in which 70.1 grams of MnSO4 is needed, but the only jar of reagent in the lab is labelled manganese(II) sulfate monohydrate. How many grams of the hydrate must the student weigh out in order to get the desired amount of the anhydrous compound?

A food chemist determines the concentration of acetic acid in a sample of apple vinegar by acid-base titration. The density of the sample is 1.01 g/mL. The titrant is 1.006 M NaOH. The average volume of titrant required to titrate 25.00 mL subsamples of the vinegar is 20.78 mL. What is the concentration of acetic acid in the vinegar? Express your answer the way a food chemist probably would: as percent by mass.

A solution is prepared by dissolving 23.7 g of CaCl2 in 375 g of water. The density of the resulting solution is 1.05 g/mL. The concentration of CaCl2 is __________ % by mass.(i) 0.0632 (ii) 6.32 (iii) 6.24 (iv) 594 (v) 0.0594

The iron in a 6.655-g sample containing some Fe 2O3 is reduced to Fe2+. The Fe2+ is titrated with 15.67 mL of 0.1517M K2Cr2O7 in an acid solution. 6Fe2+ + Cr2O72- + 14H+ → 6Fe3+ + 2Cr3+ + 7H2O(l) Find the mass of Fe. Find the percentage of Fe.