Figure 5. Clock-wise from the upper left: While atomic mass and molar mass are numerically equivalent, keep in mind that they are vastly different in terms of scale, as represented by the vast difference in the magnitudes of their respective units amu versus g. To appreciate the enormity of the mole, consider a small drop of water weighing about 0. If the molecules were distributed equally among the roughly seven billion people on earth, each person would receive more than billion molecules.
Figure 6. The number of molecules in a single droplet of water is roughly billion times greater than the number of people on earth. The mole is used in chemistry to represent [latex]6. Watch this video to learn more. For example, if we know the mass and chemical composition of a substance, we can determine the number of moles and calculate number of atoms or molecules in the sample.
According to nutritional guidelines from the US Department of Agriculture, the estimated average requirement for dietary potassium is 4.
What is the estimated average requirement of potassium in moles? The mass of K is provided, and the corresponding amount of K in moles is requested. Referring to the periodic table, the atomic mass of K is The given mass of K 4. The calculated magnitude 0.
Beryllium is a light metal used to fabricate transparent X-ray windows for medical imaging instruments. How many moles of Be are in a thin-foil window weighing 3. A liter of air contains [latex]9. What is the mass of Ar in a liter of air? The molar amount of Ar is provided and must be used to derive the corresponding mass in grams. Since the amount of Ar is less than 1 mole, the mass will be less than the mass of 1 mole of Ar, approximately 40 g.
The result is in agreement with our expectations as noted above, around 0. Copper is commonly used to fabricate electrical wire Figure 7. How many copper atoms are in 5. Figure 7. Copper wire is composed of many, many atoms of Cu. Considering that the provided sample mass 5. Carrying out the two-step computation yields:.
The factor-label method yields the desired cancellation of units, and the computed result is on the order of 10 22 as expected.
A prospector panning for gold in a river collects How many Au atoms are in this quantity of gold? Our bodies synthesize protein from amino acids. One of these amino acids is glycine, which has the molecular formula C 2 H 5 O 2 N. How many moles of glycine molecules are contained in We can derive the number of moles of a compound from its mass following the same procedure we used for an element in Example The molar mass of glycine is required for this calculation, and it is computed in the same fashion as its molecular mass.
One mole of glycine, C 2 H 5 O 2 N, contains 2 moles of carbon, 5 moles of hydrogen, 2 moles of oxygen, and 1 mole of nitrogen:. How many moles of sucrose, C 12 H 22 O 11 , are in a g sample of sucrose? Vitamin C is a covalent compound with the molecular formula C 6 H 8 O 6. The recommended daily dietary allowance of vitamin C for children aged 4—8 years is [latex]1.
As for elements, the mass of a compound can be derived from its molar amount as shown:. The molar mass for this compound is computed to be Performing the calculation, we get:.
A packet of an artificial sweetener contains Given that saccharin has a molar mass of How many carbon atoms are in the same sample? How many C 4 H 10 molecules are contained in 9. How many hydrogen atoms? The brain is the control center of the central nervous system Figure 8. It sends and receives signals to and from muscles and other internal organs to monitor and control their functions; it processes stimuli detected by sensory organs to guide interactions with the external world; and it houses the complex physiological processes that give rise to our intellect and emotions.
The broad field of neuroscience spans all aspects of the structure and function of the central nervous system, including research on the anatomy and physiology of the brain.
Figure 8. Specialized cells called neurons transmit information between different parts of the central nervous system by way of electrical and chemical signals. Chemical signaling occurs at the interface between different neurons when one of the cells releases molecules called neurotransmitters that diffuse across the small gap between the cells called the synapse and bind to the surface of the other cell.
These neurotransmitter molecules are stored in small intracellular structures called vesicles that fuse to the cell wall and then break open to release their contents when the neuron is appropriately stimulated. This process is called exocytosis see Figure 9. One neurotransmitter that has been very extensively studied is dopamine, C 8 H 11 NO 2.
Dopamine is involved in various neurological processes that impact a wide variety of human behaviors. Figure 9. One important aspect of the complex processes related to dopamine signaling is the number of neurotransmitter molecules released during exocytosis. Since this number is a central factor in determining neurological response and subsequent human thought and action , it is important to know how this number changes with certain controlled stimulations, such as the administration of drugs.
It is also important to understand the mechanism responsible for any changes in the number of neurotransmitter molecules released—for example, some dysfunction in exocytosis, a change in the number of vesicles in the neuron, or a change in the number of neurotransmitter molecules in each vesicle.
Significant progress has been made recently in directly measuring the number of dopamine molecules stored in individual vesicles and the amount actually released when the vesicle undergoes exocytosis. Analysis of these neurons from mice subjected to various drug therapies shows significant changes in the average number of dopamine molecules contained in individual vesicles, increasing or decreasing by up to three-fold, depending on the specific drug used.
These studies also indicate that not all of the dopamine in a given vesicle is released during exocytosis, suggesting that it may be possible to regulate the fraction released using pharmaceutical therapies. The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass.
A convenient amount unit for expressing very large numbers of atoms or molecules is the mole. Experimental measurements have determined the number of entities composing 1 mole of substance to be [latex]6. The mass in grams of 1 mole of substance is its molar mass. Determine the number of moles of each component.
From the moles, calculate the number of atoms and the mass of the elements involved. Zirconium: [latex]0. Determine the molar mass and, from the grams present, the moles of each substance. The compound with the greatest number of moles of Al has the greatest mass of Al.
Determine the number of grams present in the diamond and from that the number of moles. Determine the molar mass of sugar. Therefore, Skip to main content. Composition of Substances and Solutions. Search for:. Example 1 Computing Molecular Mass for a Covalent Compound Ibuprofen, C 13 H 18 O 2 , is a covalent compound and the active ingredient in several popular nonprescription pain medications, such as Advil and Motrin.
Solution Molecules of this compound are comprised of 13 carbon atoms, 18 hydrogen atoms, and 2 oxygen atoms. Following the approach described above, the average molecular mass for this compound is therefore: Check Your Learning Acetaminophen, C 8 H 9 NO 2 , is a covalent compound and the active ingredient in several popular nonprescription pain medications, such as Tylenol.
Example 2 Computing Formula Mass for an Ionic Compound Aluminum sulfate, Al 2 SO 4 3 , is an ionic compound that is used in the manufacture of paper and in various water purification processes. Following the approach outlined above, the formula mass for this compound is calculated as follows: Check Your Learning Calcium phosphate, Ca 3 PO 4 2 , is an ionic compound and a common anti-caking agent added to food products.
Example 3 Deriving Moles from Grams for an Element According to nutritional guidelines from the US Department of Agriculture, the estimated average requirement for dietary potassium is 4. Solution The mass of K is provided, and the corresponding amount of K in moles is requested.
Example 4 Deriving Grams from Moles for an Element. Solution The molar amount of Ar is provided and must be used to derive the corresponding mass in grams.
Answer : [latex]4. Solution We can derive the number of moles of a compound from its mass following the same procedure we used for an element in Example 3: The molar mass of glycine is required for this calculation, and it is computed in the same fashion as its molecular mass. Example 7 Deriving Grams from Moles for a Compound.
Solution As for elements, the mass of a compound can be derived from its molar amount as shown: The molar mass for this compound is computed to be Performing the calculation, we get: [latex]1.
Therefore, you will have 0. Related questions How do you calculate the number of moles from volume? How do you convert grams to mole? Question e5. Question 8d48c. Why is the mole an important unit to chemists? What's the mole number?
How does the mole relate to carbon 12? How does the mole relate to molecules and ions? How do you calculate the moles of a substance?
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