Post-Lecture Chapter 02 Desc Chem
Use the figure to calculate the mass of mercuric oxide that would be needed to produce 100.0 g of mercury metal.
(100.0 g mercury metal) x (100.00 grams of mercuric oxide / 92.61 grams of mercury) m = 107.98 g
How many atoms of sulfur are there in one mole of sulfur dioxide?
6.02×10^23 atoms of sulfur
What is the mass of lithium relative to carbon-12?
6.94/12.00
What is the mass of lithium relative to carbon?
6.94/12.01
A sulfur dioxide molecule is made up of one sulfur atom and two oxygen atoms. What is the mass of one mole of sulfur dioxide?
64.06 g
Using Döbereiner's triadic relationship, calculate the mass of Ga based on Mendeleev's values from his periodic table.
70.2 amu
Using Döbereiner's triadic relationship, calculate the mass of Ga based on values in the modern periodic table.
70.90 amu
What was Democritus's contribution to atomic theory?
Democritus described the tiny ultimate particle as "atomos" (which means "cannot be cut").
According to the law of definite proportions, a chemical compound is made up of elements proportioned in specific ratios. For example, carbon dioxide has the chemical formula CO2. In 1 mol of CO2, there are 12 g of carbon and 32 g of oxygen. The ratio of the mass of carbon to oxygen in CO2 is 12:32, or 3:8. A sample of ammonia contains 9.0 g of hydrogen and 42 g of nitrogen. Another sample of the same compound contains 15.0 g of hydrogen. Calculate the amount of nitrogen in the second sample of ammonia.
Mass of nitrogen in the second sample = 70 g
Why did the idea that matter was continuous (rather than atomic) prevail for so long?
Matter appears continuous, and without experimental chemistry, there is no way to prove that matter is not continuous.
Why is it important to recycle mercury-based fluorescent light bulbs instead of putting them in landfills?
Mercury is toxic and can leach from landfills into groundwater.
Classify the following as atoms or molecules.
Molecules: CO N2 NH3 Atoms: Mg, P
As early as 400 B.C., Greek philosophers proposed that matter was made up of particles. During the 1800s, John Dalton linked the idea of atoms with the chemical identity of an element. His atomic theory of matter involved the following postulates. Each element is composed of extremely small particles called atoms. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of other elements. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. Scientists later discovered isotopes, which showed that the second postulate was not entirely true, and nuclear reactions, which showed that the third postulate was not true. Which of the following reactions is possible according to Dalton's atomic theory?
N2+O2→2NO
Calculate the mass ratio of S to O in SO, and then calculate the mass ratio of S to O in SO2, given that the mass of S is approximately 32 g and the mass of O is approximately 16 g. What is the whole number multiple that describes the relationship between the sulfur-to-oxygen mass ratios of each sample?
Whole number multiple = 2
Two different compounds are obtained by combining oxygen with nitrogen. The first compound results from combining 53.3 g of O with 46.7 g of N, and the second compound results from combining 82.0 g of O and 17.9 g of N. What is the whole number multiple that describes the relationship between the oxygen-to-nitrogen mass ratios in each sample?
Whole number multiple = 4
Two compounds, V and W, are composed only of hydrogen and carbon. Compound V is 80.0% carbon by mass and 20.0% hydrogen by mass. Compound W is 83.3% carbon by mass and 16.7% hydrogen by mass. What is the ratio of masses of hydrogen in these compounds given a fixed mass of carbon?
a) 1.00 : 1.25
How many moles of carbon are there in a 9.000 g (45.00 carat) diamond?
0.7493 moles
How many atoms of oxygen are there in one mole of sulfur dioxide?
1.20×10^24 atoms of oxygen
Magnesium oxide decomposes into magnesium and oxygen. If 4.03 g of magnesium oxide decomposes to form 2.43 g of magnesium, what mass of oxygen gas is also released in the reaction?
1.60 g
Matter is neither created nor destroyed in a chemical reaction. Thus, the mass of the products of a chemical reaction must be equal to the mass of the starting materials. Formally, this concept is called the law of conservation of mass. A sample of sodium reacts completely with 568 g of chlorine, forming 936 g of sodium chloride. What mass of sodium reacted?
368 g
From how many atoms of carbon is this diamond composed?
4.51×10^23atoms
When carbon is burned in air, it reacts with oxygen to form carbon dioxide. When 13.2 g of carbon were burned in the presence of 53.5 g of oxygen, 18.3 g of oxygen remained unreacted. What mass of carbon dioxide was produced?
48.4 g
The smallest building blocks of matter are atoms. All matter in the universe, including you and me, are made of atoms. Atoms are so small that 7.5 trillion carbon atoms could fit on the period at the end of this sentence. A sample of hydrogen, H, will contain only hydrogen atoms. Similarly, samples of other elements contain only atoms of that element. An atom is composed of even smaller particles such as protons, electrons, and neutrons. Atoms of elements can bond together to form molecules and compounds. For example, an atom of carbon combines with two atoms of oxygen to form a molecule of carbon dioxide, CO2. A molecule is the smallest unit of a compound. Molecules are made up of a group of atoms tightly bonded together. A molecule of an element is made up of the same kind of atoms, such as Cl2 and a molecule of a compound is made up of different kinds of atoms, such as NH3. Since the molecule is made up of atoms, it can be separated back into its original form—atoms—through chemical means. Molecular formulas use chemical symbols. For example, in a molecule of Cl2, the first letter is uppercase and the second letter is lowercase. The symbol Cl represents only one element, which is chlorine, and a subscript 2 represents the number of atoms of chlorine in the molecule. Consider another example, a molecule of ammonia represented as NH3. Since both the elements are written in uppercase, the molecule has two different atoms—one atom of nitrogen and three atoms of hydrogen. Classify the following statements as describing atoms, molecules, or both.
Atoms: Smallest unit of an element Molecules: Smallest unit of a compound Combination of atoms of the same or different elements Both: Divisible by chemical or nuclear means Smallest unit that can be isolated through physical changes
Why does the glass of water weigh less after the pill has dissolved?
Carbon dioxide gas will be generated and released as the anti-acid pill dissolves.
Two experiments were conducted: 1.375 g of copper(II) oxide, CuO2, was reduced by heating at high pressure with excess hydrogen to yield 1.098 g of copper Cu. 1.179 g of copper Cu was dissolved in nitric acid to yield copper(II) nitrate, which was converted to 1.476 g copper(II) oxide, CuO2, on ignition. Show that the results illustrate the law of definite proportions by calculating the percentage of oxygen in copper(II) oxide in experiments 1 and 2.
Explanation: Mass of oxygen present = mass of copper(ll) oxide - mass of copper residue = 1.375 - 1.098 =0.277 Percentage of oxygen = 0.277/1.375 * 100 = 20.14% for experiment 1 For experiment 2 Mass of oxygen present = 1.476 - 1.179 = 0.297 Percentage by mass of oxygen present in the copper (ll) oxide = 0.297/1.476 × 100 = 20.12% It will be noticed that though the source of the copper ll oxide was different, they still contain the same proportion of oxygen which verify the law of definite proportion which states that all pure sample of the same chemical compound contain similar elements combined in the same proportion by mass. Percentage of oxygen in sample 1, sample 2 = 20.15%, 20.12%
Mendeleev wrote chemical formulas using superscripts to indicate the number of atoms of each element in the compound. Modern practice is to reserve superscripts for charges, and subscripts denote the number of each element in a chemical formula. For example, we would write N2O, not N2O, to indicated two nitrogen atoms. Using Mendeleev's table, predict the formula, using subscripts to denote the number of each atom in the formula, for oxides of carbon (C) and aluminum (Al).
Oxide of C,Al =CO2,Al2O3
When two elements combine to form two different compounds, the mass ratio of the elements in one compound is related to the mass ratio of elements in the other compound by a small whole number. If two elements A and B combine to form two compounds AB and AB2 then the ratio of the mass of B to A in AB2 and the mass of B to A in AB will be a simple whole number. Watch the animation to learn more about this relationship when carbon reacts with oxygen to form more than one compound. When carbon is oxidized in a small amount of oxygen, the principle product formed is carbon monoxide (CO) according to the simplified equation O2(g)+2C(s)→CO(g)O2(g)+2C(s)→CO(g) When the oxidation occurs in a higher concentration of oxygen, the principle product formed is carbon dioxide (CO2) O2(g)+C(s)→CO2(g)O2(g)+C(s)→CO2(g) The mass ratio of oxygen to carbon in carbon dioxide (CO2) is twice the mass ratio of oxygen to carbon in carbon monoxide (CO). Identify the statements that are correct based on the video.
Part A The mass ratio of oxygen to carbon in CO2 is 2.667 for every sample of CO2. For two compounds of C and O, the mass ratio of C to O in one compound is a multiple of the mass ratio of C to O in the other compound. The mass ratio of oxygen to carbon in CO is 1.33 for every sample of CO.
Give two examples of how green chemistry has helped to reduce the use of cadmium in consumer products.
Substitution of metal hydrides for cadmium in batteries. Compounds with lower toxicity now substitute for cadmium pigments in plastics.
Distinguish between the atomic view and the continuous view of matter.
The Atomic theory assumes that matter is made up of small unit particles that cannot be further subdivided and still be the same kind of matter.
Distinguish between the ancient Greek definition of an element and the modern one.
The Greeks believed that there were four basic elements: earth, air, fire, and water.
In an experiment illustrated at right, about 15 mL of hydrochloric acid solution was placed in a flask and approximately 3 g of sodium carbonate was put into a balloon. The opening of the balloon was then carefully stretched over the top of the flask, taking care not to allow the sodium carbonate to fall into the acid in the flask. The flask was placed on an electronic balance, and the mass of the flask and its contents was found to be 38.61 g. The sodium carbonate was then slowly shaken into the acid. The balloon began to fill with gas. When the reaction was complete, the mass of the flask and its contents, including the gas in the balloon, was found to be 38.61 g. What law does this experiment illustrate? Explain?
The Law of Conservation of Mass. This experiment demonstrates The Law of Conservation of Mass, because as a chemical reaction happens, mass cannot be created, nor destroyed. Hence, why the mass remained 38.61 grams.
Please explain how the following two combustion (burning) reactions appear to disobey the law of conservation of mass. When a diamond is burned, the mass that remains is zero. b. When a piece of wood is burned, the leftover ashes weigh less than the wood. Upon further investigation, it is noted that CO2 is vented off from both reactions. With this additional information, state how you can prove the diamond is made of pure carbon and yet the wood is not
a) The carbon, which forms the diamond, has been converted to carbon dioxide and escaped into the atmosphere. (b) The carbon in the wood is converted to carbon dioxide, but the residual ash is not. 3. Burning the diamond in an enclosed environment would trap the carbon dioxide for further analysis.
What discoveries finally refuted the idea?
law of definite proportions and law of multiple proportions
If you place a 3.00 g effervescent antacid pill into 110 mL (110 g ) of water in a 100 g glass, how much will the glass of water weigh once the antacid pill has dissolved?
less than 213 g
Nitrous oxide (N2O, "laughing gas") contains 28.01 g of nitrogen in every 44.01 g of nitrous oxide. What mass of nitrous oxide can be formed from 38.7 g of nitrogen?
m = 60.8 g
Before the beginning of the 18th century, only a few elements were known. As the discovery of new elements increased during the 1800s, scientists attempted to develop a simple method of arranging the elements to better understand their properties and the properties of their compounds. Though scientists were able to classify elements into broad categories, they struggled to come to a consensus on how to most effectively group the elements. Gradually, they started grouping the elements based on their relative atomic masses. A Russian chemist, Dmitri Mendeleev, published his version of the systematic arrangement of elements in 1869. There were only 63 known elements during his time, and he arranged them in increasing order of their atomic masses. The periodic table is a tabular arrangement of elements according to their chemical properties. Mendeleev's periodic table gained wide acceptance because he accounted for unidentified elements and also grouped the elements with similar chemical properties. In a few cases, he did this despite the order of their atomic masses. Today, the periodic table consists of 118 elements. Identify the factors that guided Mendeleev while classifying the elements.
organizing by increasing atomic mass grouping of similar elements together
