General Chemistry Answers

Chemist to determine copper concentration in rock sample. Knowing copper undergoes redox reactions, they chose to use iodometric titration for analysis. Unknown sample weighing 1.5098g was acidified with 3.0M H2SO4 to dissolve copper compounds and diluted with 30mL distilled water. This was followed by addition of excess KI producing I2 and CuI precipitate from Cu2+(Reaction 1). Then, liberated I2 reacted with excess KI forming triiodide anion(Reaction 2), which was titrated with Na2S2O3 titrant(Reaction 3). This entire solution required 17.60 mL of titrant to reach starch end point.

MW: Cu (63.546)

a. Write balanced chemical equation for Reactions 1-3

b. Write mole ratio between Cu2+ and S2O32–

Prior to titration of sample, titrant was standardized by taking 50.0 mL of 6.7863x10-3M standard KIO3 solution, acidifying, and adding KI crystals. Titration of this solution required 9.80mL to reach starch endpoint.

c. Write concentration of S2O32– titrant in M

d. Write copper content of rock sample in %w/w

why is it that when you try to boil an egg in an open pot, and leave awhile, upon returning you've noticed the water decreases? what about the movement of water molecules? what if you decided to put a lid on the pot, what will be the movement of the water molecules?

What is the weight percent (w/w) of NaOH in a solution prepared by dissolving 30.0g of NaOH in 120.0g of H₂O?

While work‎ing in a metal proc‎essing facility, Letlen had accide‎ntally mixed two me‎tal vats toge‎ther rea‎ting an alloy. On‎e vat ‎was lab‎eled for cadmium, w‎hile the other was not. It can be ass‎umed that he‎se are of pure metal comp‎osition. To identify this metal, Letlen took 1.000 g of the homogenous alloy ample composed of cadmium and the unknown metal, dissolved, and diluted it to exactly 100.0 mL in a volumetric flask. A 20.00-mL aliquot was taken and titrated this using 22.82 mL of 0.05000 M EDTA

MW: Cd (112.411 g/mol)

a. Calcul‎ate the moles of Cd and the m‎oles of unkno‎wn metal in the 20.00‎-mL aliquot.

b. Calc‎ulate the mo‎les of Cd and the mo‎les of unk‎nown metal in the s‎ample.

c. Calc‎ulate the mass (in g) of Cd and the m‎ass (in g) of unk‎nown metal in the sam‎ple.

d. Wh‎at is the MW (in g/mol) of the unkn‎own met‎al?

e. What is the ide‎ntity of the unkno‎wn met‎al that Letlen accid‎entally mix‎ed?

Two analy‎sts deter‎mined compos‎ition of a 2.500-g s‎oda ash sa‎mple. They divid‎ed s‎ample into two equa‎l 1.250-g par‎ts and analyz‎ed it separa‎tely through do‎uble indi‎cator titrat‎ion.

One of them dissolved sample in water to prepare a 250.0 mL stock solution. A 50.00 mL aliquot was titrated using 0.10 M HCl. A volume of 40.08 mL was measured using phenolphthalein indicator and 13.58 mL with the methyl orange indicator.

Another al‎so also dissolved sample in water to prepare a 250.0 mL stock solution. However, they spilled the primary standard, 100% pure Na2CO3, in the solution. They titrated a 50.00 mL aliquot using 0.10 M HCl same way first one did. For methyl orange indicator, they measured a volume of 30.07 mL

MW: NaOH (40.00 g/mol), Na2CO3 (105.99), NaHCO3 (84.01)

a. What is/are component/s of original soda ash sample?

b. What is/are %composition (in %w/w) of original soda ash sample?

c. How much Na2CO3 (in grams) did second spill in solution?

Hint: You do not need vph to solve this

How many moles are in 987.0 grams of Ra(OH)2

1. Coal gasification converts coal into a combustible mixture of carbon monoxide and hydrogen, called coal gas, in a gasifier: H2Oq) + C(s) –→ CO(g)+ H2(g) AHo = ? Calculate the standard enthalpy change for this reaction from the following chemical equations: 2 C(s) + O2(g)→ 2 CO(g) AHo = -222 kJ 2 H2(g) + O2(g) → H2O1) → 2H2O(g) AHo = -484 kJ H2O(g) AHo = +44 kJ This coal gas can be used a fuel: CO(g) + H2(g) + O2(g) CO2(g) + H2O(g) 2. Predict the change in enthalpy for this combustion reaction from the following equations: 2 C(s) + O2(g) → 2 CO(g) AHo = -222 kJ C(s) + O2(g) 2 Н(9) + Ог(g) → CO2(g) AHo = -394 kJ 2H2O(g) AHo = -484 kJ 3. Use the following calorimetrically determined enthalpy changes to predict the standard enthalpy change for the reaction of ethene with chlorine gas. C2H4(g) + Cl2(g) → C2H3C1(g) + HCl(g) AHo = ? H2(g) + Cl2(g) → 2HCI(g) AHo = -185 kJ C2H4(g) + HCl(g) → C2H5C11) AHo = -65 kJ C2H3C1(g) + H2(g) → C2H5C14) AH. = -140 kJ

Sodium carbonate reacts with Sulphuric Acid. What is the balance chemical equation for the reaction?

Given the following reaction:

N2 (g) + 3H2 (g) → 2NH3 (g)

How would the rate of change for NH3 compare to the rate of change for N2?

1. What are buffers?

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2. Write equations to show the dissociation of the salts (i) ammonium chloride and (ii) sodium acetate.

I. __________________________________________________________________

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II. __________________________________________________________________

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3. Write equations to show the hydrolysis of the two salts named in Exercise 2.

I. __________________________________________________________________

II. ________________________________________________________________

4. Calculate the pH of the ammonium chloride solution of concentration 0.1M if the acid dissociation constant/ hydrolysis constant for the NH₄⁺ ion is 5.8 x 10^-10