Question

Oliver likes to go fishing in the river by his house. One day he noticed that there was a white substance on some rocks at the bottom of the river. When he looked closely, it appeared as though someone had sprinkled a powder or crystals in the water. Moreover, the substance was found mainly where a small creek joined the larger river.

Curious, Oliver followed the creek through the forest toward an industrial area. Eventually, he reached a fence and found the source of the creek water — a large drainage pipe. Oliver noticed that there was steam coming off the water as it flowed out of the metal pipe.

The temperature reading (in ^oC) of the water that flowed out of the drainage pipe: 88.35

The temperature reading (in ^oC) of the water in the river: 7.14

Analysis at four differnt points along the creek and river revealed that the chemical potassium nitrate was found in the water.

1. Explain what is happening, in general terms, by applying your understanding of solutions and solubility.
2. Use the information provided to calculate the concentration of the solution in parts per million (ppm).
   • Point A: 14.7 g of KNO_3(aq) in 1.00 x 10³ L of H₂O_(l)
   • Point B: 1.12 g of KNO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Point C: 200 mg of KNO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Point D: 0.061 g of KNO_3(aq) in 1.00 x 10¹ L of H₂O_(l)

   Note that 1 ml of water has a mass of 1 g.

   In addition to potassium nitrate, analysis revealed there was four other chemicals found in the water at Point A.

3. Use the information provided to calculate both the molar mass and molarity for each chemical found in the water.
   • Sodium sulfate: 25.8 g of Na₂SO_4(aq) in 1.00 x 10¹ L of H₂O_(l)
   • Sodium carbonate: 582.2 mg of Na₂CO_3(aq) in 1.00 x 10² L of H₂O_(l)
   • Barium chloride: 6.8 mg of BaCl_2(aq) in 1.00 x 10³ L of H₂O_(l)
   • Magnesium phosphate: 212 g of Mg₃(PO₄)_2(aq) in 1.00 x 10¹ L of H₂O_(l)
   Potassium nitrate: 14.7 g of KNO_3(aq) in 1.00 x 10³ L of H₂O_(l)
4. The pipe used by the factory was made of an alloy of steel (Iron (Fe) = 90%, Carbon (C) = 8.5%, Manganese (Mn) = 1.5%). What amount (in kilograms) of each element was found in the pipe if it has a mass of 24.9 kg?
5. An alloy of gold contains 65% gold (Au), 16.5% silver (Ag), and some copper (Cu). What amount of copper would you expect in 59.8 g of this gold alloy?

Answer 1

Answer

Part 1 i.e concentration of KNO3 in parts per million at each point:

Given : 1 ml is equal to 1 gm

Point A 14.7 g of KNO3 in 1 x 10 3 l of water     ( 1 L= 1000Ml)

i.e. 14.7 grams of KNO3 in 1000000000 ml of water

Parts of million = mass of solute in mg/ mass of solution in l

=14700/ 1000

=14.7 ppm

POINT B

Mass of KNO3 = 1.12 g in 1 x 10 2 L of water

Concentration in ppm

=1120 / 100

=11.2 ppm

POINT C

Mass of KNO3 = 200 mg in 1x 10 2 L of water

=200 /100

=2 ppm

POINT D

Mass of KNO3 =0.061 g in 1x 10 1 L of water

=61/10

=6.1ppm

By observing the obtained values, we can say that at different points, solubility of KNO3 in water is different. Solubility of KNO3 increases with increase in temperature.

PART 2

Calculation of molar mass and molarity: ( atomic masses of Na=23, Sulphur=32, oxygen=16, Barium= 137, chlorine=35.5, carbon=12, magnesium=24, phosphorus=31)

1. 25.8 g sodium sulphate in 1x 10 1 l of water

Molar mass of sodium sulphate(Na2SO4) = 23x2+32+64

                                                        = 142

Molarity= mass of solute in grams/ molar mass of solute x volume of solution in litres

                = (25.8/142) x 10

                = 1.817M

1. 582.2 mg of sodium carbonate in 10 2 l of water

        Molar mass of Sodium carbonate ( Na2CO3)= 23 x2 + 12+ 3 x 16

                                                                             = 106

Molarity= 0.5822/ 106 x 10 2

               = 0.549M

1. 6.8 grams of barium chloride in 10 3 l of water

Molar mass of barium chloride (BaCl2) = 137 + 2 x 35.5

                                                                     = 208

Molarity = (6.8/208) x 10 3

                = 32.692M

        4 14.7 g of magnesium phosphate in 10 3 litres of water

              Molar mass of magnesium phosphate [ Mg3(PO4)2 = 3 x 24 + 2 ( 31 + 4x 16)

                                                                                                        = 264

               Molarity= 14.7 / 264 x 10 3

                           =55.682M

PART 3

Pipe used contains

Fe =90%, C= 8.5%, Mn= 1.5%

Mass of pipe = 24.9kg

1. Mass of Fe= (90/100)x 24.9 = 22.41Kg
2. Mass of C = (8.5/100) x 24.9= 2.1165Kg
3. Mass 0f Mn = (1.5/ 100)x 24.9= 0.3735Kg

PART 4

An alloy of gold contains gold = 65% , silver= 16.5% and copper=?

Mass of alloy= 59.8 grams

Mass of copper= ?

Solution: Percentage of copper = 100- (65 + 16.5)

                                                            = 18.5%

               Mass of copper= (18.5/100) x 59.8

                                             = 11.063 grams