1) Cobalt has a mass number of 59 and an atomic number of 27. A student wants to create a model of a cobalt atom. Which statement about the model is correct?(1 point)
A. The model should show 27 protons and 32 neutrons.******
B. The model should show 59 protons and 27 neutrons.
C. The model should show 27 protons and 27 neutrons.
D. The model should show 32 protons and 59 neutrons.
2) In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?(1 point)
A) The chemical formula for lithium sulfide is LiS2.
B) The atoms in lithium sulfide are held together by bonds.*****
C) Both lithium and sulfur form positive ions.
D) A molecular model of lithium sulfide would have two spheres.
3)Which element has the same number of valence electrons as bromine (Br)? (1 point)
A) ytterbium (Yb)
B) selenium (Se)
C) krypton (Kr)******
D) astatine (At)
4) Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
A) They have similar reactivity.*******
B) They are both hard and brittle.
C) They have similar atomic weights.
D) They are both colorless.
5) A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
A) It is a chemical change because there is no phase change.
B) It is a chemical change because the size changes.
C) It is a physical change because the process is reversible.
D) It is a physical change because there is no reaction.******
6) How are chemical changes different from physical changes?(1 point)
A) They form new substances.********
B) They are reversible.
C) They involve heat.
D) They include shifts in the phase of matter.
7)A scientist makes several observations about a chemical reaction and records them in the table shown. Which observation contains an error? (1 point) picture added!
A) 1
B) 3
C) 2******
D) 4
8) In a chemical reaction, hydrofluoric acid (HF) and sodium hydroxide (NaOH) combine to form sodium fluoride (NaF) and water (H2O). The reaction uses 20 grams of hydrofluoric acid and 40 grams of sodium hydroxide, and it produces 18 grams of water. How much sodium fluoride does the reaction produce?(1 point)
A) 60 grams
B) 42 grams
C) 18 grams******
D) 78 grams
9)Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)
A) Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
B) Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.********
C) Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
D) Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
10) One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)
A) two******
B) four
C) three
D) six
11) Use the unbalanced chemical equation to answer the question.
2NaHCO3 → Na2CO3 + CO2
What can be added to the products to balance the equation? (1 point)
A) CH2OH****
B) H2O
C) H2
D) O2
12) The chemical formula for phosphorus trichloride is PCl3. In one to two sentences, explain how you would build a ball-and-stick model of phosphorus trichloride. Include a description of the parts of the model.(2 points)
13) Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the chemical equation. A scientist adds 4 grams of Cu to 2 grams of S to start the reaction. At the end of the experiment, she has 6 grams of product. In one to two sentences, explain what would happen if the scientist increased the amount of copper to 6 grams, and why. (1 point)
12) To build a ball-and-stick model of phosphorus trichloride (PCl3), place a larger sphere representing the central phosphorus atom and attach three smaller spheres representing the chlorine atoms to it using sticks to represent chemical bonds. The model should show the arrangement of the atoms and the bonds between them.
13) If the scientist increased the amount of copper to 6 grams in the reaction with sulfur, more copper sulfide would be produced. This is because the amount of product formed in a chemical reaction is directly proportional to the amount of reactants.
1) The model should show 27 protons and 32 neutrons. This is because the atomic number, which represents the number of protons in an atom, is 27. The mass number, which represents the total number of protons and neutrons in an atom, is 59. Therefore, to find the number of neutrons, we subtract the atomic number from the mass number (59 - 27 = 32).
2) The atoms in lithium sulfide are held together by bonds. This is because lithium (Li) and sulfur (S) have different electronegativities, causing them to form ionic bonds. In an ionic bond, one atom donates electrons to another atom, resulting in the formation of ions. In this case, lithium (Li) donates one electron to sulfur (S), forming a positively charged lithium ion (Li+) and a negatively charged sulfide ion (S2-).
3) Krypton (Kr) has the same number of valence electrons as bromine (Br). Both elements are in Group 17 of the periodic table, also known as the halogens. Elements in Group 17 have seven valence electrons, which is the number of electrons in the outermost energy level of an atom. Therefore, krypton (Kr) would have the same number of valence electrons as bromine (Br).
4) Sodium (Na) and potassium (K) are in the same group on the periodic table because they have similar reactivity. Elements within the same group of the periodic table have the same number of valence electrons, which determines their chemical properties. Sodium (Na) and potassium (K) both belong to Group 1, also known as the alkali metals, and they have one valence electron. Because they have similar electronic configurations, they exhibit similar chemical behavior and reactivity.
5) The act of cutting fabric into two pieces is a physical change. A physical change refers to a change in the form or state of matter without the formation of new substances. In this case, the fabric only changes in size or shape, but its chemical composition remains the same. It can easily be reversed by sewing or reattaching the two pieces.
6) Chemical changes are different from physical changes because they form new substances. During a chemical change, the bonds between atoms are broken and rearranged, resulting in the formation of new compounds or molecules. This involves a change in the chemical composition and properties of the substances involved. Physical changes, on the other hand, do not involve the formation of new substances and only involve changes in the physical properties such as size, shape, or phase of matter.
7) Observation 2 contains an error. According to the table provided, the student recorded the color of the solution as "blue-black" before the reaction and "green" after the reaction. However, this observation is incorrect because the color change from blue-black to green indicates a change in color and therefore must be recorded as a separate observation.
1) To determine the correct model of a cobalt atom, we need to understand its atomic structure. The atomic number of cobalt is 27, which tells us that it has 27 protons in its nucleus. The mass number is the sum of protons and neutrons, so in this case, it is 59. Therefore, the correct statement is that the model should show 27 protons and 32 neutrons (A).
2) Lithium sulfide is a compound composed of lithium (Li) and sulfur (S) atoms. The chemical formula for lithium sulfide is Li2S, indicating that there are two atoms of lithium and one atom of sulfur. In a molecule of lithium sulfide, the atoms are held together by chemical bonds (B).
3) To find an element with the same number of valence electrons as bromine (Br), we need to look for an element in the same group on the periodic table. Bromine belongs to group 7A (or 17), and elements in the same group have the same number of valence electrons. Among the given options, krypton (Kr) is in the same group as bromine and has the same number of valence electrons (C).
4) Sodium (Na) and potassium (K) are in the same group (group 1A or 1) on the periodic table. Elements in the same group have similar reactivity because they have the same number of valence electrons, which determines their chemical behavior. Therefore, the correct answer is that sodium and potassium are in the same group because they have similar reactivity (A).
5) When a student cuts fabric into two pieces, it is a physical change. A physical change involves a change in the physical properties of a substance without forming new substances. Cutting the fabric does not involve any chemical reaction, and the fabric can still be put back together, making it a physical change (D).
6) Chemical changes are different from physical changes because they result in the formation of new substances. During a chemical change, the chemical composition of the substance changes, leading to the formation of different substances with different properties (A).
7) Without the table mentioned in the question, it is not possible to determine which observation contains an error. Please provide the table or specific observations for further analysis.
8) To determine the amount of sodium fluoride (NaF) produced in the chemical reaction, we need to balance the equation and use stoichiometry. From the equation, we can see that the ratio between hydrofluoric acid (HF) and sodium fluoride (NaF) is 2:1. Given that 18 grams of water is produced, which is a byproduct, we can determine that the reaction produces an equal amount of NaF. Therefore, the correct answer is 18 grams (C).
9) To demonstrate the conservation of matter during a physical change, we need to compare the mass of the initial substance with the mass of the final substance. Option B provides the correct procedure to demonstrate conservation of matter during a physical change – finding the mass of a raw egg and comparing it to the mass of the cooked egg. If the mass remains the same, it indicates that matter is conserved during the physical change (B).
10) To determine the number of atoms in the products, we need to calculate the total number of each type of atom. One molecule of bromine (Br2) contains two bromine atoms. Two molecules of potassium chloride (KCl) contain two potassium atoms and two chlorine atoms. Therefore, the total number of atoms in the products is two (A).
11) The given chemical equation, 2NaHCO3 → Na2CO3 + CO2, is unbalanced. To balance the equation, we need to add coefficients in front of the chemical formulas. In this case, we need to add a coefficient of 2 in front of NaHCO3 to balance the equation. Therefore, the correct answer is H2O (B) because it can be added to the products to balance the equation.
12) To build a ball-and-stick model of phosphorus trichloride (PCl3), you will need three different components: Phosphorus (P) atoms and chlorine (Cl) atoms, represented by different colored balls, and sticks to represent the covalent bonds between the atoms. Start by placing a phosphorus atom in the center and three chlorine atoms around it, connecting them with sticks to represent the chemical bonds.
13) If the scientist increased the amount of copper from 4 grams to 6 grams in the reaction with sulfur, more copper sulfide would be formed because the reaction is determined by the limiting reactant. Sulfur is the limiting reactant in this case because the moles of sulfur are insufficient to react completely with the moles of copper. Increasing the amount of copper would allow sulfur to react more fully, resulting in the formation of more copper sulfide. Therefore, if the scientist used 6 grams of copper, more than 6 grams of product would be obtained.