Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 4: Problem 127

x H2O. A 4.93-g sample of Epsom salts was heated to drive off the water of hydration. The ma… # Epsom salts is a hydrated ionic compound with the following formula: MgSO4 # x H2O. A 4.93-g sample of Epsom salts was heated to drive off the water of hydration. The mass of the sample after complete dehydration was 2.41 g. Find the number of waters of hydration (x) in Epsom salts

Short Answer

Expert verified
The number of waters of hydration (x) in Epsom salts is 7.

Step by step solution

01

Determine the mass of water lost

Subtract the mass of the dehydrated salt from the original mass of the hydrated salt to find the mass of water lost. This is calculated by 4.93 g - 2.41 g.
02

Calculate the molar mass of MgSO4

Use the periodic table to find the molar mass of MgSO4: (Mg = 24.31) + (S = 32.07) + 4(O = 15.999) = 120.37 g/mol.
03

Calculate the moles of MgSO4

Divide the mass of anhydrous MgSO4 by its molar mass to find the moles of MgSO4 present: 2.41 g / 120.37 g/mol.
04

Calculate the moles of water lost

Calculate the mass of water lost and then find the moles of water, using the molar mass of water (18.015 g/mol): (4.93 g - 2.41 g) / 18.015 g/mol.
05

Determine the number of moles of water per mole of MgSO4 (x)

Divide the moles of water lost by the moles of MgSO4 to find the ratio x which is the number of water molecules per formula unit of MgSO4.
06

Round x to the nearest whole number

Because x must be a whole number (you can't have a fraction of a water molecule in a formula unit), round the previous result to the nearest whole number to find the chemical formula of hydrated Epsom salts.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Water of Hydration
In chemistry, water of hydration refers to water molecules that are chemically bound within the structure of a compound. These molecules are not part of the compound's actual chemical formula but are locked into the crystal structure when the compound forms. During a process like heating, these water molecules can be removed—a process known as dehydration. To determine the number of waters of hydration in a compound like Epsom salt (MgSO4 · xH2O), you can weigh the compound before and after heating and calculate the change in mass, which is attributed to the loss of water.
Molar Mass
The molar mass of a substance is the mass of one mole of that substance—the molecular or formula weight expressed in grams. The molar mass is vital for converting between grams and moles of a substance, since it indicates how much one mole of a substance weighs. To calculate it for a compound, you need to sum the atomic masses (from the periodic table) of each element in the compound, multiplied by the number of atoms of that element present in the formula. For Epsom salts (anhydrous MgSO4), the molar mass is calculated using the atomic weights of magnesium, sulfur, and oxygen.
Moles Calculation
The concept of moles calculation is essential in chemistry for quantifying the amount of a substance. A mole is a unit that measures the number of particles, whether they are atoms, molecules, ions, or electrons, in a substance. The number is defined as Avogadro's number (approximately 6.022 x 1023 particles). To calculate moles from mass, you divide the mass of the substance by its molar mass. In our example with Epsom salts, after finding the anhydrous mass of MgSO4, we use its molar mass to calculate the number of moles of anhydrous MgSO4 present.
Stoichiometry
Stoichiometry involves the calculation of reactants and products in chemical reactions. It's based on the conservation of mass and the concept of moles. In the context of hydrates, stoichiometry enables us to relate the moles of water lost during heating to the moles of the anhydrous compound. This provides the stoichiometric ratio necessary to determine the number of water molecules associated with each formula unit of the compound, and hence, identify the formula of the hydrated compound. This step-by-step stoichiometric analysis is critical in identifying the value of x in our Epsom salt problem, which represents the number of water molecules per formula unit.
Empirical Formula Determination
Determining the empirical formula of a compound involves finding the simplest whole-number ratio of atoms present in the compound. For a hydrated ionic compound, this also includes determining the number of water molecules associated with each unit of the compound, known as the water of hydration. The procedure involves calculating the moles of each element and water, then finding the simplest mole ratio. For example, in the case of Epsom salts, once we determine the moles of MgSO4 and the moles of water, we can translate these into the mole ratio and round it off to the nearest whole number to find the empirical formula for the hydrated compound.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

The molar mass and empirical formula of several compounds are listed. Find the molecular formula of each compound. a. C4H9, 114.22 g>mol b. CCl, 284.77 g>mol c. C3H2N, 312.29 g>mol

Because of increasing evidence of damage to the ozone layer, chlorofluorocarbon (CFC) production was banned in 1996. However, there are about 100 million auto air conditioners in operation that still use CFC-12 (CF2Cl2). These air conditioners are recharged from stockpiled supplies of CFC-12. If each of the 100 million automobiles contains 1.1 kg of CFC-12 and leaks 25% of its CFC-12 into the atmosphere per year, how much chlorine, in kg, is added to the atmosphere each year due to auto air conditioners? (Assume two significant figures in your calculations.)

Create a flowchart with a series of simple questions that can be used to determine whether a chemical formula is that of an atomic element, a molecular element, a molecular compound, or an ionic compound. Use your flowchart to identify the correct category for P4, KCl, CH4, Ne, and NH4NO3.

Determine the number of moles (of molecules or formula units) in each sample. a. 25.5 g NO2 b. 1.25 kg CO2 c. 38.2 g KNO3 d. 155.2 kg Na2SO4

A 2.52-g sample of a compound containing only carbon, hydrogen, nitrogen, oxygen, and sulfur is burned in excess oxygen to yield 4.23 g of CO2 and 1.01 g of H2O. Another sample of the same compound, of mass 4.14 g, yields 2.11 g of SO3. A third sample, of mass 5.66 g, yields 2.27 g of HNO3. Calculate the empirical formula of the compound. (Hint: Use the first set of data to determine % C and % H by mass. Use the second and third sets of data to determine % S and % N by mass. Then determine % O by mass by difference from 100%.)
See all solutions

Recommended explanations on Chemistry Textbooks

Making Measurements

Read Explanation

Inorganic Chemistry

Read Explanation

Physical Chemistry

Read Explanation

Kinetics

Read Explanation

Chemistry Branches

Read Explanation

Ionic and Molecular Compounds

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free