Determine the formula of a hydrate (questions only)


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Example #1: A 15.67 g sample of a hydrate of magnesium carbonate was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?

Example #2: A hydrate of Na2CO3 has a mass of 4.31 g before heating. After heating, the mass of the anhydrous compound is found to be 3.22 g. Determine the formula of the hydrate and then write out the name of the hydrate.

Example #3: When you react 3.9267 grams of Na2CO3 · nH2O with excess HCl(aq), 0.6039 grams of a gas is given off. What is the number of water molecules bonded to Na2CO3 (value of n)?

Example #4: If 1.951 g BaCl2 · nH2O yields 1.864 g of anhydrous BaSO4 after treatment with sulfuric acid, calculate n.

Example #5: Given that the molar mass of Na2SO4 · nH2O is 322.1 g/mol, calculate the value of n.

Example #6: 4.92 g of hydrated magnesium sulphate crystals (MgSO4 nH2O) gave 2.40 g of anhydrous magnesium sulfate on heating to a constant mass. Determine the value of n.

Bonus Example: 3.20 g of hydrated sodium carbonate, Na2CO3 nH2O was dissolved in water and the resulting solution was titrated against 1.00 mol dm-3 hydrochloric acid. 22.4 cm3 of the acid was required. What is the value of n?


Go to hydrate problems #1 - 10

Problem #1: Anhydrous lithium perchlorate (4.78 g) was dissolved in water and re-crystalized. Care was taken to isolate all the lithium perchlorate as its hydrate. The mass of the hydrated salt obtained was 7.21 g. What hydrate is it?

Problem #2: A substance was found to have the following percentages by mass: 23% zinc; 11% sulfur; 22% oxygen; 44% water. What is the empirical formula?

Problem #3: A 5.00 g sample of hydrated barium chloride, BaCl2 · nH2O, is heated to drive off the water. After heating, 4.26 g of anhydrous barium chloride, BaCl2, remains. What is the value of n in the hydrate's formula?

Problem #4: A 1.98 g sample of a cobalt(II) chloride hydrate is heated over a burner. When cooled, the mass of the remaining dehydrated compound is found to be 1.55 g. What is the formula for the original hydrate? How can you make sure that all of the water of hydration has been removed?

Problem #5: A solution was made by dissolving 52.0 g of hydrated sodium carbonate in water and making it up to 5.00 dm3 of solution. The concentration of the solution was determined to be 0.0366 M. Determine the formula of hydrated sodium carbonate.

Problem #6: Determine the formula and name for the hydrate: 73.42% ammonium phosphate and 26.58% water.

Problem #7: 5.00 g of borax (Na2B4O7 · 10H2O) was heated to remove the water. What is the mass of anhydrous sodium tetraborate that remains?

Problem #8: A sample of hydrate lost 14.75% of its original weight during heating. Determine the number of moles of hydration per mole of anhydrous substance if the molecular weight of the anhydrate is 208 grams/mole.

Problem #9: 1.33g of hydrated ethanedioic acid (H2C2O4 nH2O) were dissolved in distilled water and the solution made up to 250.0 mL in a graduated flask. 25.0 mL of this solution were titrated by 21.1 mL of 0.100M NaOH. Calculate the number of moles of water of crystallization in the hydrated ethanedioic acid.

Problem #10: A solution was made by dissolving 71.5 g of hydrated sodium carbonate in water and making up to 5.00 dm3 of solution. The concentration of a 25.0 cm3 portion was determined to be 0.04805 M. Use the information to find the waters of hydration of the hydrated sodium carbonate.

Bonus Problem: A certain quantity of sodium carbonate decahydrate was heated to remove the water. The mass of the anhydrous compound that remained was 2.764 g. What was the original mass of the hydrated sodium carbonate?


Go to hydrate problems #11 - 20

Problem #11: 6.9832 g of FeSO4 xH2O is dissolved in water acidified with sulfuric acid. The solution is made up to 250. cm3. 25.00 cm3 of this solution required 25.01 cm3 of 0.0200 M KMnO4 to titrate completely. Calculate x.

Problem #12: A 81.4 gram sample of BaI2 2H2O was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, how many grams of the anhydrous compound remained?

Problem #13: If the hydrated compound UO2(NO3)2 9H2O is heated gently, the water of hydration is lost. If you heat 4.05 mg of the hydrated compound to dryness, what mass of UO2(NO3)2 will remain?

Problem #14: Here is a Yahoo Answers problem with two solutions. One of them is mine.

Problem #15: How many grams of water and anhydrous salt would you get when heating 9.42 g of Fe(NO3)3 9H2O?

Problem #16: Heating 0.695 g CuSO4 nH2O gives a residue of 0.445 g. Determine the value of n.

Problem #17: Epsom salt is MgSO4 nH2O. The hydrate was found to contain 71.4% oxygen. Calculate the number of water molecules associated with each formula unit of magnesium sulfate hydrate.

Problem #18: A sample of hydrated magnesium sulphate, MgSO4 · nH2O, is found to contain 51.1% water. What is the value of n?

Problem #19: If a 9.15 g sample of a hydrated salt produced 6.50 g of anhydrous salt (309.650 g/mol) and 2.65 g of water (18.015 g/mol), what is the molecular mass of the hydrated salt?

Problem #20: A hydrated compound has the formula MCl2 · 2H2O. In an experiment, the following data were determined:

mass of the hydrate: 1.000 g
mass of H2O: 0.185 g

Determine the identity of element M from these results.

Problem #21: A 0.256 g sample of CoCl2 yH2O was dissolved in water, and excess silver salt was added. The silver chloride was filtered, dried, and weighed, and it had a mass of 0.308 g. What is the value of y?

Problem #22: A sample of 0.416 g of CoCl2 yH2O was dissolved in water, and an excess of sodium hydroxide (NaOH) was added. The cobalt hydroxide salt was filtered and heated in a flame, forming cobalt(III) oxide (Co2O3). The mass of cobalt(III) oxide formed was 0.145 g. What is the value of y?


The Yahoo Answers problem: A crystalline hydrated zinc sulfate salt has the chemical formula ZnSO4 · xH2O, where x is the number of water molecules attached. 8.2 grams of this salt was heated to evaporate the water until 4.6 grams remained. (a) Work out the mass of water evaporated. (b) Work out the value of x in the formula ZnSO4 · xH2O.