Chapter 16: Problem 116
A 1.294 -g sample of a metal carbonate \(\left(\mathrm{MCO}_{3}\right)\) is reacted with \(500 \mathrm{~mL}\) of a \(0.100 \mathrm{M} \mathrm{HCl}\) solution. The excess \(\mathrm{HCl}\) acid is then neutralized by \(32.80 \mathrm{~mL}\) of \(0.588 M \mathrm{NaOH} .\) Identify M.
Short Answer
Expert verified
The metal M is likely to be magnesium (Mg) given that the molar mass of magnesium is approximately 24.30 g/mol, which is close to the calculated molar mass of M (24.19 g/mol).
Step by step solution
01
Identify Important Reactions
Two reactions are taking place here - \n1. The reaction between \(\mathrm{MCO}_{3}\) and \(\mathrm{HCl}\), and \n2. The reaction between \(\mathrm{HCl}\) and \(\mathrm{NaOH}\). \nThe reactions can be represented as follows: MCO3 + 2HCl --> MCl2 + CO2 + H2O HCl + NaOH --> NaCl + H2O
02
Calculate moles of HCl neutralized by NaOH
Since we know the volume and molarity of NaOH used to neutralize the excess HCl, we can find the number of moles of HCl neutralized. The moles of a solution equals the molarity multiplied by the volume (in liters). So the moles of HCl neutralized by NaOH is \(0.588 M * 32.80 mL = 0.0193 moles\)
03
Calculate Total moles of HCl
The given volume of HCl is 500 mL and its molarity is 0.1 M. Multiplying volume and molarity gives the total moles of HCl \(0.100 M * 500 mL = 0.050 moles\)
04
Calculate moles of HCl reacted with MCO3
Subtracting the moles of HCl that remained for the NaOH from the total moles of HCl will give the number of moles that reacted with the MCO3. The moles of HCL that reacted with the MCO3 equals \(0.050 moles - 0.0193 moles = 0.0307 moles\)
05
Determining moles of MCO3
From the balanced equation of the reaction between MCO3 and HCl, we see that one mole of MCO3 reacts with 2 moles of HCl. Hence the moles of MCO3 that reacted with HCl equals moles of HCl divided by 2. So the moles of MCO3 is \(0.0307 moles/2 = 0.01535 moles\)
06
Calculate the Molar mass of M
The molar mass of a substance is its mass divided by its moles. Given the mass of MCO3 is 1.294g and its moles are 0.01535, the molar mass of MCO3 will be: \(1.294g/0.01535 = 84.20 g/mol\). However, this includes the molar mass of CO3 which accounts for 60.01 g/mol. Thus, the molar mass of M will be \(84.20 g/mol - 60.01 g/mol\) = \(24.19 g/mol\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Molecular Molarity
Molecular molarity is a measure of the concentration of a solution, indicating how many moles of a substance are present in a liter of solution. It is denoted by the symbol 'M' and is calculated by dividing the number of moles of solute by the volume of solution in liters. For example, a 0.100 M HCl solution contains 0.100 moles of hydrogen chloride dissolved in each liter of solution. Practically, when we say we're using 500 mL of 0.100 M HCl, we imply there are (0.500 L) (0.100 moles/L) = 0.050 moles of HCl in our reaction mixture.
When dealing with chemical reactions, knowing the molarity of reactants is crucial as it allows us to calculate how many moles of reactants will participate in the reaction, and thereby, how many moles of the products will be formed. This is particularly significant in stoichiometry and is the starting point in solving problems like the one in our exercise.
When dealing with chemical reactions, knowing the molarity of reactants is crucial as it allows us to calculate how many moles of reactants will participate in the reaction, and thereby, how many moles of the products will be formed. This is particularly significant in stoichiometry and is the starting point in solving problems like the one in our exercise.
The Basics of Acid-Base Neutralization
Acid-base neutralization is a type of chemical reaction in which an acid reacts with a base to produce water and an ionic compound called a salt. In the context of the exercise, neutralization occurs when the excessive hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH). The neutralization reaction can be represented as HCl + NaOH → NaCl + H2O.
Determining the amount of NaOH needed to neutralize the excess HCl involves mole calculations. By using the molarity of the NaOH solution and the volume used, students can compute the moles of HCl that were neutralized. It's an essential step in the problem-solving process, as it leads to understanding how much acid initially reacted with the metal carbonate and, thus, to identification of the unknown metal.
Determining the amount of NaOH needed to neutralize the excess HCl involves mole calculations. By using the molarity of the NaOH solution and the volume used, students can compute the moles of HCl that were neutralized. It's an essential step in the problem-solving process, as it leads to understanding how much acid initially reacted with the metal carbonate and, thus, to identification of the unknown metal.
Mole Calculation in Chemical Reactions
Mole calculation is fundamental in chemical stoichiometry as it helps in quantifying the amount of reactants and products in a chemical reaction. One mole is Avogadro's number (approximately 6.022 x 10^23) of particles, be it atoms, molecules, or ions. In the provided exercise, mole calculations are used to bridge the gap between the macroscopic measurements that we can observe (like weight and volume) and the microscopic world of individual atoms and molecules.
For instance, knowing the molarity and volume of NaOH used, students can find the number of moles of NaOH and therefore the moles of HCl it neutralized. This is done using the formula: moles = molarity (M) volume (L). Such calculations enable us to understand and predict how different substances will react together in a given stoichiometric proportion defined by the balanced chemical equation.
For instance, knowing the molarity and volume of NaOH used, students can find the number of moles of NaOH and therefore the moles of HCl it neutralized. This is done using the formula: moles = molarity (M) volume (L). Such calculations enable us to understand and predict how different substances will react together in a given stoichiometric proportion defined by the balanced chemical equation.
Determining Molar Mass
Molar mass determination is the process of calculating the mass of one mole of a substance. The molar mass is usually expressed in grams per mole (g/mol) and can be found by adding the atomic masses of the elements that make up the compound. In the exercise, the molar mass determination is a vital step in identifying the unknown metal M in the metal carbonate (MCO3).
Once the number of moles of MCO3 has been calculated, the molar mass is found by dividing the given mass in grams by the number of moles. Subtracting the molar mass of the carbonate ion (CO3) from the molar mass of metal carbonate gives the molar mass of the metal alone. The students can then use the periodic table to match this calculated molar mass with a known element, thus identifying the metal M.
Once the number of moles of MCO3 has been calculated, the molar mass is found by dividing the given mass in grams by the number of moles. Subtracting the molar mass of the carbonate ion (CO3) from the molar mass of metal carbonate gives the molar mass of the metal alone. The students can then use the periodic table to match this calculated molar mass with a known element, thus identifying the metal M.