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The formula for percent hydrate is calculated by taking the mass of the water lost and dividing by the mass of the hydrate.
1. To calculate the water lost, subtract the value for the mass of the anhydrate (substance after it has been heated and dried [without water]) from the value for the mass of the hydrate (substance before it has been heated [with water]).
Mass hydrate - mass anhydrate = water lost
OR, another way to put it
Mass before heating - mass after heating = water lost
2. Next, divide the mass of the water lost by the mass of the hydrate.
Mass water lost
- mass hydrate
Ex. A student was asked to identify an unknown hydrate by following the procedure described in this module. After heating and cooling, a 2.752g sample of this unknown weighed 1.941g. Students were given a list of possible compounds from which to identify their unknowns:
LiNO3 * 3 H2O
Ca(NO3)2 * 4 H2O
Sr(NO3)2 * 4 H2O
In order to identify the unknown substance, the percent hydrate for the following compounds listed above needs to be calculated. This is done by first calculating the molar mass of each hydrate, then calculating the percent of water in each hydrate.
Before proceeding, the amount of water lost needs to be calculated, followed by calculating the percent water in the unknown hydrate.
Water lost: 2.752g hydrate - 1.941g anhydrate = 0.811g
Percent water of hydrate: 29.47%
0.811g
2.751g x 100%
1. Identify the molar mass of each hydrate.LiNO3 * 3 H2O (Lithium Nitrate Trihydrate)Molar Mass of LiNO3 (Lithium Nitrate): 68.9459g
Molar Mass of 3 H2O (Water): 18.0152 * 3 OR 54.0456g
Molar Mass of LiNO3 * 3 H2O = 122.9915g (add values above, not multiply!)
Ca(NO3)2 * 4 H2O (Calcium Nitrate Tetrahydrate)
Molar Mass of Ca(NO3)2 (Calcium Nitrate): 164.0878g
Molar Mass of 4 H2O (Water): 18.0152 * 4 OR 72.0608g
Molar Mass of Ca(NO3)2 * 4 H2O = 236.1486g
Sr(NO3)2 * 4 H2O (Strontium Nitrate Tetrahydrate)
Molar Mass of Sr(NO3)2 (Calcium Nitrate): 211.6298g
Molar Mass of 4 H2O (Water): 18.0152 * 4 OR 72.0608g
Molar Mass of Sr(NO3)2 * 4 H2O = 283.6906g
2. Calculate the percent water in each hydrate.Percent Water of Hydrate LiNO3 * 3 H2O (Lithium Nitrate Trihydrate)- 54.0456g
122.9915g x 100 = 43.94%
Percent Water of Hydrate Ca(NO3)2 * 4 H2O (Calcium Nitrate Tetrahydrate)
- 72.0608g
236.1486g x 100 = 30.52%
Percent Water of Hydrate Sr(NO3)2 * 4 H2O (Strontium Nitrate Tetrahydrate)
- 72.0608g
283.6906g x 100 = 25.40%
Due to the closest comparison in percentage values, the most likely compound is Ca(NO3)2 * 4 H2O (Calcium Nitrate Tetrahydrate). The values aren't exact matches probably because the water was not fully evaporated while being heated (leading calculations to indicate less water than there really was/is in substance). In other words, due to errors made on behalf of the experiment conductor by not completely heating the substance.
Calculating Molar Mass of Substances
Element A: Number Atoms Element A x Atomic Mass Element A = Mass A
Element B: Number Atoms Element B x Atomic Mass Element B = Mass B
etc.
Add all of the mass values found above (Mass A + Mass B ...) and you have the value of molar mass. In the case above, to find the molar mass of the hydrates, simply add the molar mass of water (multiply by however many water molecules are in compound) and the molar mass of the other compound.
What else can I help you with?
What is the percent of the mystery substance?
I'm unable to calculate the percentage of an unknown substance without more information about its composition or quantity.
If you had an unknown substance and were asked to identify it would you use the intensive or extensive properties of the substance?
To identify an unknown substance, you would typically use its intensive properties. Intensive properties, such as density, boiling point, and specific heat, are independent of the amount of substance present and are useful for identifying specific materials.
What is the probable identity of the unknown crystalline hydrate?
The probable identity of the unknown crystalline hydrate can be determined by conducting techniques such as X-ray crystallography, spectroscopy, and elemental analysis. These methods can provide information on the crystal structure, chemical composition, and properties of the compound, which can help in identifying the hydrate.
Why are a substance's physical properties a reliable means to identify it?
A substance's physical properties, such as color, density, melting point, and solubility, are determined by the arrangement of its atoms and molecules. These properties are unique to each substance and do not change regardless of the amount or form of the substance present. Therefore, by comparing the physical properties of an unknown substance to those of known substances, we can reliably identify it.
What are the usefulness of density in identification of unknown substance?
Density can help identify an unknown substance by comparing its measured density to known values for different materials. Substances have unique densities due to their composition and structure, allowing for classification based on this property. By determining the density of an unknown substance and comparing it to reference values, one can begin to narrow down potential identities.
Knowing the solubility of an unknown substance in water can help to identify what it is.?
Knowing the solubility of an unknown substance in water can help you calculate its molarity. It is however important to get its weight first.
How can one identify an unknown substance in chemistry?
One can identify an unknown substance in chemistry by conducting various tests such as spectroscopy, chromatography, and chemical reactions to determine its properties and compare them to known substances.
What properties do scientists look for to identify an unknown substance?
Scientists look for properties such as density, boiling point, melting point, solubility, conductivity, and reactivity to help identify an unknown substance. By comparing these properties to known data in a database, scientists can often determine the identity of the unknown substance.
How can one test an unknown substance to identify it?
To identify an unknown substance, one can conduct tests such as spectroscopy, chromatography, and chemical reactions to determine its properties and composition. These tests can help determine the substance's characteristics and compare them to known substances for identification.
An unknown hydrate ac xH2O has a mass of 1.632 g and the anhydrous compound AC has a mass of 1.008 g What is the experimental percentage of water in the hydrate?
To find the experimental percentage of water in the hydrate, we need to calculate the mass of water lost during dehydration. Mass of water lost = 1.632 g - 1.008 g = 0.624 g Experimental percentage of water = (mass of water lost / initial mass of hydrate) x 100% = (0.624 g / 1.632 g) x 100% ≈ 38.24%
What is the percent of the mystery substance?
I'm unable to calculate the percentage of an unknown substance without more information about its composition or quantity.
What happens when you add sodium carbonate to an unknown substance?
Sodium carbonate can react with acidic components in the unknown substance to form carbon dioxide gas, which may result in fizzing or effervescence. This reaction can help identify the presence of acidic compounds in the unknown substance.
Why Do You Think Scientists Can Use The Basic Properties Of Matter To Help Identify An Unknown Substance?
Because if a substance can't be known then it has to prove its mass and volume
What can be used to identify an unknown substance?
Just about any property that can be observed or measured can help you reduce the number of options.
How can density be used to determine the identity of a substancce?
Density can be used to determine the identity of a substance by comparing the density of the unknown substance to the known densities of different substances. Each substance has a characteristic density, so if the density of the unknown substance matches that of a known substance, it can help identify the unknown substance.
Why is it important to identify an unknown substance?
Because the substance could potentially be extremely toxic or harmful. You must never use an unknown substance in experiments without identifying it first, many tests can be undertaken to determine the cation and anion. These tests include the flame test, solubility tests, precipitate reaction tests and conductivity tests. These do vary depending on the unknown substance.
If you had an unknown substance and were asked to identify it would you use the intensive or extensive properties of the substance?
To identify an unknown substance, you would typically use its intensive properties. Intensive properties, such as density, boiling point, and specific heat, are independent of the amount of substance present and are useful for identifying specific materials.
