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Example Questions
Example Question #441 : Ap Chemistry
Consider the reaction of potassium carbonate with calcium nitrate to form potassium nitrate and calcium carbonate:
Suppose 50ml of a 0.250M potassium carbonate solution was mixed with 100ml of a 0.175M calcium nitrate solution. What is the maximum amount of calcium carbonate that could be obtained?
First, we must determine how many moles of each reactant begin the reaction by multiplying the molarity by the volume. Don't forget to convert volume to liters!
Next, use the reaction coefficients (i.e. the stoichiometry) to determine how many moles of calcium carbonate could be formed from each of the reactants. In this case, there is a 1:1 molar ratio between both reactants and calcium carbonate.
Thus, 0.0125 moles of potassium carbonate could form 0.0125 moles of calcium carbonate, while 0.0175 moles of calcium nitrate could form 0.0175 moles of calcium carbonate. The maximum amount of product is going to be determined by the limiting reactant, i.e. the reactant that provides the least amount of product. In this case, the limiting reactant is potassium carbonate, and the maximum yield of calcium carbonate is 0.0125mol.
For the final step convert this value to grams:
Example Question #1 : The Periodic Table
Which of the following atoms is the largest?
Potassium
Nitrogen
Oxygen
Bromine
Lithium
Potassium
Atom size is determined by the number of shells and how many protons and electrons are present in the atom. Any atom in a higher number period (row) is larger than any atom in a lower number period, since the number of electron shells increases as the number of the period increases. Within the same period, atoms get smaller as you move towards the right. This is because the atomic number increases, increasing the number of protons in the nucleus. These protons attract the surrounding electrons, pulling them in closer, and shrinking the total size of the atom.
In general, atomic radius will increase as you move down and to the left. This makes helium the smallest atom and francium the largest.
Example Question #1 : The Periodic Table
Which ion of nitrogen is the largest?
Ions of atoms vary in their size. When an atom gains electrons the atomic size increases, and when an atom loses electrons the atomic size decreases. Nitrogen with a formal charge of negative three will have the largest size because it has the most electrons. Remember that adding electrons will cause a negative ion, while removing electrons will cause a positive ion.
Example Question #2 : The Periodic Table
Which of the following values will decrease as you move left to right in a period of the periodic table?
Electronegativity
Atomic radius
Atomic number
Electron affinity
Atomic radius
Moving left to right on the periodic table causes an increase in atomic number (number of protons) as well as electron affinity and electronegativity.
Atomic radius, however, will decrease when moving left to right. As more protons are added to the nucleus, they have a stronger attraction to the electrons. This pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.
Example Question #1 : The Periodic Table
Elements that have similar properties will have the same __________ on the periodic table.
atomic charge
atomic mass
atomic radius
group
period
group
The periodic table is set up so that we can quickly tell which elements will react in a similar chemical fashion. The elements from the same group, that is the same column, will have similar properties. This is due to the same number of valence electrons in the outer shell.
Example Question #4 : The Periodic Table
Elements from which group in the periodic table will have the lowest first ionization energies?
Halogens
Group III
Alkali metals
Alkaline earth metals
Noble gases
Alkali metals
Ionization energy is the amount of energy needed to remove an electron from an atom. Alkali metals only need to lose one electron in order to achieve the stable noble gas octet. As a result, the loss of this electron requires very little energy since the resulting ion is favorably stable. This property causes alkali metals (found in group I) to have the lowest first ionization energies.
Example Question #1 : Identifying Periodic Trends
Which of these elements has the smallest atomic radius?
Phosphorus
Bismuth
Antimony
Nitrogen
Arsenic
Nitrogen
The trend for atomic radius is as follows: atomic radius increases from right to left within a row and from top to bottom within a group on the periodic table.
Example Question #3 : The Periodic Table
Which of these elements is the most electronegative?
Boron
Nitrogen
Carbon
Fluorine
Oxygen
Fluorine
Fluorine is the most electronegative element. The trend for electronegativity is as follows: electronegativity increases from left to right within a row and from bottom to top within a group of the periodic table.
Example Question #4 : Identifying Periodic Trends
Which of these elements is the least electronegative?
Rubidium
Francium
Cesium
Sodium
Potassium
Francium
Francium is the least electronegative element. The trend for electronegativity is as follows: electronegativity increases from left to right within a row and from bottom to top within a group of the periodic table.
Example Question #5 : Identifying Periodic Trends
Which of these elements has the largest atomic radius?
Phosphorus
Silicon
Chlorine
Aluminum
Sulfur
Aluminum
The trend for atomic radius is as follows: atomic radius increases from right to left within a row and from top to bottom within a group on the periodic table.
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