Periodic table molar mass

All molar masses quoted in this text refer to these average values. Their values are given in Appendix 2D. They are also included in the periodic table inside the front cover and in the alphabetical list of elements inside the back cover. 

STRATEGY First, the limiting reactant must be identified (Toolbox M.l). This limiting reactant determines the theoretical yield of the reaction, and so we use it to calculate the theoretical amount of product by Method 2 in Toolbox L.l. The percentage yield is the ratio of the mass produced to the theoretical mass times 100. Molar masses are j calculated using the information in the periodic table inside the front cover of this i book. 

A radius of 128 pm corresponds to 1.28 X 10-8 cm, and the molar mass of copper (from the periodic table on the inside front cover) is 63.55 g-mol. The predicted density is therefore... 

Suppose that 10.0 g of an organic compound used as a component of mothballs is dissolved in 80.0 g of benzene. The freezing point of the solution is 1.20°C. (a) What is an approximate molar mass of the organic compound (b) An elemental analysis of that substance indicated that the empirical formula is C3H2C1. What is its molecular formula (c) Using the atomic molar masses from the periodic table, calculate a more accurate molar mass of the compound. 

For purposes of chemical bookkeeping, it is unnecessary to know the isotopic molar masses and isotopic distributions of the elements. All we need to know is the mass of one mole of an element containing its natural composition of isotopes. These molar masses usually are included in the periodic table, and they appear on the inside front and back covers of this textbook. 

Our task is to estimate the volume occupied by one atom of lithium. As usual, the mole is a convenient place to begin the calculations. Visualize a piece of lithium containing one mole of atoms. The molar mass, taken from the periodic table, tells us the number of grams of Li in one mole. The density equation can be used to convert from mass to volume. Once we have the volume of one mole of lithium, we divide by the number of atoms per mole to find the volume of a single atom. 

Our modem periodic table was developed independently in the late 1860s by Dimitri Mendeleev (Russian) and Julius Lothar Meyer (German). At that time, about 60 elements had been discovered, but nothing was known about atomic stracture. Lothar Meyer and Mendeleev had to work with elemental molar masses and other known elemental properties. 

Mendeleev was bolder in his interpretation than Lothar Meyer, and for this reason we honor him as the primary discoverer of the modem periodic table. A few elements did not fit the pattern of variation in combining numbers with molar mass. Mendeleev proposed that these irregularities meant that the element s molar mass had been measured incorrectly. For example, Mendeleev predicted that the correct molar mass of indium is 113 g /mol, not 75 g /mol, the value assigned at that time on the assumption that the formula for indium oxide is InO. Later experiments showed that the correct formula is L12 O3, and indium s tme molar mass is 114.8 g/mol. 

Mendeleev also predicted the existence of elements that had not yet been discovered. His arrangement of the then-known elements left some obvious holes in the periodic table. For instance, between zinc (combines with 2 Cl) and arsenic (combines with 5 Cl) were holes for one element that would combine with three chlorine atoms and another that would combine with four. Mendeleev assigned these holes to two new elements. He predicted that one element would have a molar mass of 68 g/mol and chemical properties like those of aluminum, while the other would have a molar mass of 72 g /mol and chemical properties similar to silicon. These elements, gallium (Z = 31, M M = 69.7 g/mol) and germanium (Z = 32, M M — 72.6 g/mol), were discovered within 15 years. Chemists soon verified that gallium resembles aluminum in its chemishy, while germanium resembles silicon, just as Mendeleev had predicted. 

Water shows properties that are interestingly different compared with hydrides of the neighbouring elements of the first row of the periodic table. Some of these properties are given in Table 3.2. From this table, water can be seen to have a very high melting point and a very high boiling point for its relative molar mass. Indeed, it is the only one of the hydrides of the... 

This will give us the moles of calcium hydroxide instead of the grams, thus we need to add another step. We have moles and we need grams, the molar mass relates these two quantities. We determine the molar mass by using the formula and the atomic weights found in a table such as the periodic table. 

You know the enthalpy change for the reaction of two moles of A1 with one mole of CI2. From the periodic table, you know the molar mass of Al. 

The fact that both the mole and the mass of an element are based on carbon-12 enables us to relate mole and mass. A molar mass is defined as the mass in grams of one mole of a substance, and it can be obtained directly from an element s atomic mass. We can use the elements hydrogen and nitrogen to illustrate this concept. Periodic table entries for both elements are shown below. The whole number above the element is the atomic number and gives the number of protons in the nucleus. The number below the element s symbol is the molar mass (as well as the atomic mass) ... 

H2 because hydrogen is a diatomic element. Consult your periodic table (or your memory, if you re that good) to obtain the molar masses of hydrogen gas (2.02 g/mol) and neon gas (20.18 g/mol). Finally, plug those values into the appropriate places within Grahcim s law, and you can see the ratio of effusion speed. 

After you have the molar mass, you can check the periodic table to determine the identity of the element by matching up the molar mass. No element specifically matches the 2.00 g/mol however, if you remember that hydrogen is diatomic and is always written as H2, you can identify the unknown gas as hydrogen ... 

Solve these kinds of problems by using the definition of molarity and conversion factors. In parts (b) and (c), you must first convert your mass in grams to moles. To do so, you divide by the molar mass from the periodic table (flip to Chapter 7 for details). In addition, be sure you convert milliliters to liters. 

Plug your volume and given molarity (M) values into the formula and solve. Finally, take your mole value and convert it into grams by multiplying it by the molar mass of your compound from the periodic table (as we explain in Chapter 7). 

The molar masses of elements are determined by using mass spectrometry to measure the masses of the individual isotopes and their abundances. The mass per mole of atoms is the mass of an individual atom multiplied by the Avogadro constant (the number of atoms per mole). However, there is a complication. Most elements occur in nature as a mixture of isotopes we saw in Section B, for instance, that neon occurs as three isotopes, each with a different mass. In chemistry, we almost always deal with natural samples of elements, which have the natural abundance of isotopes. So, we need the average molar mass, the molar mass calculated by taking into account the masses of the isotopes and their relative abundances in typical samples. All molar masses quoted in this text refer to these average values. Their values are given in Appendix 2D. They are also included in the periodic table inside the front cover and in the alphabetical list of elements inside the back cover. 

It is time for another look at the periodic table. Recall from Unit 1 that the larger of the two numbers in each square is called the atomic mass of the element. Molar mass is the sum of the atomic masses of all the atoms in the formula of a compound or molecule. Remember to round these atomic masses to the nearest whole number. 

Note that the molar mass was not given, but since it is needed, we can find it from the periodic table. If you have forgotten how to do this, see Chapter 14. 

To calculate a molar mass, add the total weights of all atom(s) in an element or compound. These weights are obtained from the Periodic Table of the Elements. 

While you can find the molar mass of an element just by looking at the periodic table, you need to do some calculations to find the molar mass of a compound. For example, 1 mol of beryllium oxide, BeO, contains 1 mol of beryllium and 1 mol of oxygen. To find the molar mass of BeO, add the mass of each element that it contains. 

The sample contains 0.750 mol. You can determine the molar mass of carbon dioxide from the periodic table. 

You can use what you now know about the mole to carry out calculations involving molar mass and the Avogadro constant. One mole of any compound or element contains 6.02 x 1023 particles. The compound or element has a mass, in grams, that is determined from the periodic table. 

Find a compound s molar mass using the periodic table. 

The molar mass of the empirical formula CH20, determined using the periodic table, is... 

Using a periodic table, record the molar mass of each of the gases listed in the table. 

The molar mass of a gas refers to the mass (in g) of one mole of the gas. You can calculate molar mass by adding the masses of atoms in the periodic table. You can also calculate molar mass by dividing the mass of a sample by the number of moles that are present. Molar mass is always expressed in the units g/mol. Table 12.2 summarizes molar volume, density, and molar mass. 

Step 2 Calculate the molar mass (M) of nitrogen gas, N2, using the molar mass in the periodic table. 

How do your results compare with the theoretical molar mass calculated from the periodic table ... 

To find the number of moles of iron, divide the mass by the molar mass. You can find the molar mass of iron in the periodic table 55.85 g/mol. Note If the reactant was a compound, such as FeCl2, you would need to calculate the molar mass by adding the molar masses of all the atoms. 

Step 2 Find the number of moles of magnesium. From the periodic table, the molar mass of magnesium is 24.31 g/mol. m... 

Step 4 Use the periodic table to determine the molar mass of lithium carbonate. To find the mass of lithium carbonate produced, multiply the number of moles by the molar mass. 

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