CHEM 1122 Lecture Notes - Lecture 17: Empirical Formula, Chemical Formula, Molecular Mass

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25 Oct 2016

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1 molecule of c reacts with 1 molecule of o2 to create 1 molecule of co2. 1 mol k+ = 1 mol kcl. 1 mol cl- = 1 mol kcl. 1 mol k+ = 1 mol cl- First convert 1 mol of compound/total grams of compound. Then convert mol of asked for element/mol of compound. Lastly conver how many grams of asked for element/1 mol of that element. Knowing mass is good, but to determine chemical formula with an unknown formula, you need mass ratio. Calculating mass % of x = (mass of x in grams/total mass of compound in grams) 100% Need mass of what you are looking for. Using mass % to calculate molecular formula. Chemical formula is written in molar ratios. Empirical formula = the lowest common denominator ratio of atoms in the chemical formula; the simplest whole number ratio. Molecular formula = the real number of atoms in the molecule.

Related Questions

CHM111

Q1. Which of the following contains the MOST atoms? You shouldn't need to do a calculation here.

A) 10.0 g Ne

B) 10.0 g He

C) 10.0 g Ar

D) 10.0 g Kr

E) 10.0 g Mg

Q2. How many atoms are present in 0.23 moles of Calcium?

Q3. How many atoms are present in 5.6 mg of Silicon?

Q4. How many grams of iodine do 5.6 x 10²⁵ atoms of iodine represent?

Q5. Balance the following Chemical Equations:

_____ CaC₂(s) + _____H₂O(l) ? _____ Ca(OH)₂(aq) + _____ C₂H₂(g)

_____ P₄O₁₀ + _____ H₂O? ______ H₃PO₄

___ C₃H₈O₃ + ___ O₂ ? ___ CO₂ + ___ H₂O

_____ C₄H₁₀(l) + _____ O₂(g) ? _____ CO₂(g) + _____ H₂O(g)

___ Al + ___ N₂ ? ___ Al₂N₃

___ NaN₃ ? ___ Na + ___ N₂

___ C₃H₅N₃O₉ ? ___ CO₂ + ___ N₂ + ___ H₂O + ___ O₂

Q6. Calculate the percent composition of each element in Al(NO₃)₃

Q7. A 65.0 g sample of a pure compound containing only Nickel, Oxygen and Carbon is found to contain 22.36 g Nickel and 18.27 g Carbon. What is the empirical formula of compound?

Q8. Determine the Empirical formula and Molecular formula of a compound that contains: 65.4% C, 9.15% H and 25.4% N by mass and has a molar mass of 220 g/mol.

Q9. Oxygen gas can be produced by the decomposition of KClO₃

2KClO₃ (s) ? 2 KCl + 3 O₂ (g)

How many grams of O₂ can be produced from 1.625 g of KClO₃?

Q10. Consider the following balanced reaction: 2 Fe (s) + Al₂O₃ (s) Â® 2 Al (s) + Fe₂O₃ (s)

If 6.25 moles of Fe react with 2.50 moles of Al₂O₃

Which reactant is the limiting reagent?

How many grams of Al are produced?

Q11. Consider the reaction for the manufacture of Aluminum sulfate:

2 AlCl₃ (aq) + 3 H₂SO₄ (aq) ? Al₂(SO₄)₃(aq) + 6 HCl (aq)

If 15.0 g of AlCl₃was mixed with 25.0 g of H₂SO₄, which reactant is the limiting reagent?

Calculate the theoretical yield of Al₂(SO₄)₃.

If only 18.63 g of Al₂(SO₄)₃ was produced, what is the percent yield of Al₂(SO₄)₃?

Q13. How many grams of Nickel (II) chloride are needed to prepare 100.0 ml of 0.125 M solution?

Q14. What volume of 0.125 M KMnO₄ (aq) solution can be prepared from 12.623 g of KMnO₄?

Compound Î Hrxn (kJ/mol) NH4NO3 + 25.7 KCl + 17.2 NaOH -44.5 KOH -57.6

You are given 6.7 grams of an unknown salt. You dissolve it in 54.1 mL of water. As the salt dissolves, the temperature of the solution changes from an initial temperature of 26.9Â°C to a final temperature of 53.9Â°C. Based on the chart of ÎH values and the temperature change, you can determine which salt you have. What is the temperature change? Î T = o C Tries 0/99

This is the ÎT component of the expression: qsurr = C x mass x ÎT where qsurr is the heat lost or gained by the contents of the calorimeter due to the chemical reaction. What is the mass that is changing temperature in this experiment? mass =_______ g

Assume that the heat capacity, C, of the solution is the same as that of water, C = 4.184 J/g oC. Solve for qsurr. qsurr = J Tries 0/99 What is the value of qsys? qsys = ____J

The change in enthalpy, ÎH, of this reaction is equal to qsys, since it was carried out under conditions of constant external pressure. Based on the sign of ÎH (or qsys) the dissolution of the unknown salt is . ________

When 6.7 g of salt are dissolved in 54.1 mL of water, 6880.4 J of heat are given off by the system. How much heat would be given off if only 1.00 g of salt had been dissolved in the water? qsys =_______ J/g

In the table, the ÎH values are given in kJ/mol. Convert your last answer to kJ to give kJ/g. Finally, multiply the kJ/g by the molar masses (g/mol) of possible salts, to get kJ/mol. The reaction of your unknown salt with water was exothermic. So, you will only need to look at salts with negative ÎH values. formula of unknown = ________

CHEM 1122 Lecture Notes - Lecture 17: Empirical Formula, Chemical Formula, Molecular Mass

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