Chemistry Answers

A chemist places 0.550 g KCl in a flask and adds water until the total volume is 0.900 L. Calculate the molarity of the solution.

What is the concentration in millimolar (mM)?

. 2.83 g of a sample of haematite iron ore [iron (III) oxide, Fe₂O₃] were dissolved in concentrated hydrochloric acid and the solution diluted to 250 cm³. 25.0 cm³ of this solution was reduced with tin(II) chloride (which is oxidised to Sn⁴⁺ in the process) to form a solution of iron(II) ions. This solution of iron(II) ions required 26.4 cm³ of a 0.0200 mol/dm³ potassium dichromate(VI) solution for complete oxidation back to iron(III) ions.

(a) given the half–cell reactions 

(i) Sn⁴⁺_(aq) + 2e^– ==> Sn²⁺_(aq)

and (ii) Cr₂O₇^2–_(aq) + 14H⁺_(aq) + 6e^– ==> 2Cr³⁺_(aq) + 7H₂O_(l)

deduce the fully balanced redox equations for the reactions

(i) the reduction of iron(III) ions by tin(II) ions

(ii) the oxidation of iron(II) ions by the dichromate(VI) ion

(b) Calculate the percentage of iron(III) oxide in the ore. 

8. Use the half-reaction method to balance the following equation and then identify the oxidizing and reducing agents:

Fe(OH)2 (s) + Pb(OH)3 -(aq) → Fe(OH)3 (s) + Pb(s) [basic]

In the course of doing valuable biomedical research one day, let's say you make a salt solution by adding 1 mol of NaCl to 90 g of water. 

What is the percent by mass (i.e. mass %) of the solution? 

What is the molality of a solution composed of 40.0 g sodium nitrate (NaNO3) and 500.0 g of water? 

Borax, continued:

An aqueous solution of Borax (Na2B4O7) is sometimes used to fireproof wood. 

How many moles of Na2B4O7 are in 600.0 ml of a 1.57 M Na2B4O7 solution? 

An aqueous solution of Borax (Na2B4O7) is sometimes used to fireproof wood. 

What is the molarity of 45.0 L of solution that contains 6.78 kg of Na2B4O7?

An aqueous solution of Borax (Na2B4O7) is sometimes used to fireproof wood. 

What is the molarity of 2.50 L of solution that contains 1.85 mol of Na2B4O7?  

A 9.168 M aqueous solution of H₂SO₄ has a density of 1.4987 g/ml at 20^∘

 C. How many grams of H₂SO₄ are in 50.0 g of this solution? 

You add 6.9 g of iron to 23.40 mL of water and observe that the volume of iron and water together is 24.28 mL.

Calculate the density of iron.