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?
The model should show 27 protons and 32 neutrons.
The model should show 27 protons and 27 neutrons.
The model should show 32 protons and 59 neutrons.
The model should show 59 protons and 27 neutrons
In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?
The atoms in lithium sulfide are held together by bonds.
The chemical formula for lithium sulfide is LiS2.
Both lithium and sulfur form positive ions.
A molecular model of lithium sulfide would have two spheres
Which element has the same number of valence electrons as bromine (Br)?
ytterbium (Yb)
krypton (Kr)
astatine (At)
selenium (Se)
Why are sodium (Na) and potassium (K) in the same group on the periodic table?
They have similar reactivity.
They have similar atomic weights.
They are both colorless.
They are both hard and brittle.
A student cuts some fabric into two pieces. Is this change physical or chemical?
It is a physical change because the process is reversible.
It is a physical change because there is no reaction.
It is a chemical change because the size changes.
It is a chemical change because there is no phase change.
How are chemical changes different from physical changes?
They involve heat.
They form new substances.
They include shifts in the phase of matter.
They are reversible.
Observation # Before Reaction During/After Reaction
1......mass = 30 grams.....mass = 42 grams
2......atoms of H = 5.........atoms of H = 5
3 .....no gas......................gas present
4......two types of molecules....three types of molecules
A scientist makes several observations about a chemical reaction and records them in the table shown. Which observation contains an error?
1
4
3
2
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?
60 grams
78 grams
18 grams
42 grams
Which procedure could be used to demonstrate that matter is conserved during a physical change?
Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?
two
three
six
four
Use the unbalanced chemical equation to answer the question.
2NaHCO3 → Na2CO3 + CO2
What can be added to the products to balance the equation?
O2
H2
CH2OH
H2O
Please help me someone I need help because Jiskha keeps updating and reseting so can someone please just help me.
I need help with this
I'm here to help! Let's go through each question one by one.
1. The model of a cobalt atom should show 27 protons and 32 neutrons. (Correct answer: The model should show 27 protons and 32 neutrons.)
2. The atoms in lithium sulfide are held together by bonds. (Correct answer: The atoms in lithium sulfide are held together by bonds.)
3. The element that has the same number of valence electrons as bromine (Br) is astatine (At). (Correct answer: astatine (At))
4. Sodium (Na) and potassium (K) are in the same group on the periodic table because they have similar reactivity. (Correct answer: They have similar reactivity.)
5. Cutting fabric into two pieces is a physical change because the process is reversible. (Correct answer: It is a physical change because the process is reversible.)
6. Chemical changes are different from physical changes because they form new substances. (Correct answer: They form new substances.)
7. Observation #2 contains an error because it mistakenly states that there are 5 atoms of H before and during/after the reaction. (Correct answer: 2)
8. The reaction produces 18 grams of sodium fluoride. (Correct answer: 18 grams)
9. To demonstrate the conservation of matter during a physical change, you could find the mass of a cup of water, boil the water, and then find the mass of the water that remains. (Correct answer: Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.)
10. In the reaction, one molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine to form six atoms in the products. (Correct answer: six)
11. H2O can be added to the products to balance the equation. (Correct answer: H2O)
I hope that helps! Let me know if you have any more questions.
I'm here to help! Let's go through each question one by one.
1. The correct statement about the model of a cobalt atom is: The model should show 27 protons and 32 neutrons. To determine this, you need to understand the atomic number and mass number. The atomic number (27) tells you the number of protons in the nucleus of the atom, and the mass number (59) tells you the total number of protons and neutrons. So, since atomic number = number of protons and mass number = number of protons + number of neutrons, you can calculate that the number of neutrons is 59 - 27 = 32.
2. The correct statement about lithium sulfide is: The chemical formula for lithium sulfide is Li2S. To determine this, you need to understand the composition of lithium sulfide. The formula tells you that there are two atoms of lithium (Li) and one atom of sulfur (S) in each molecule of lithium sulfide.
3. The element that has the same number of valence electrons as bromine (Br) is: astatine (At). To determine this, you need to locate bromine on the periodic table and identify its group number. Bromine is in group 17, also known as the halogens. Other elements in the same group, such as astatine (At), will have the same number of valence electrons (7 in this case).
4. Sodium (Na) and potassium (K) are in the same group on the periodic table because: they have similar reactivity. To determine this, you need to understand the properties of sodium and potassium. Both elements belong to Group 1, also known as the alkali metals, which are highly reactive metals. Therefore, they are placed in the same group because they exhibit similar reactivity.
5. The change of cutting fabric into two pieces is: a physical change because there is no reaction. To determine this, you need to understand the difference between physical and chemical changes. In a physical change, the properties of a substance change but no new substances are formed, and the change is usually reversible. Cutting fabric is a physical change because it only changes the size or shape of the fabric, but the fabric itself does not change chemically.
6. The main difference between chemical changes and physical changes is: chemical changes form new substances. To determine this, you need to understand the characteristics of chemical and physical changes. Chemical changes involve the formation of new substances with different properties, while physical changes only alter the size, shape, or state of matter without creating new substances.
7. The observation in the table that contains an error is: 4. This cannot be determined based on the information given. To determine this, you need to carefully examine each observation and compare it to the original values. Observation 1 shows an increase in mass, Observation 2 shows the same number of hydrogen atoms, Observation 3 indicates the presence of gas, but Observation 4 is not clear because it states a change in the number of molecule types without specifying which ones.
8. The amount of sodium fluoride produced in the given chemical reaction is: 18 grams. To determine this, you need to balance the chemical equation and then use the given quantities to calculate the mass of the desired product. In this case, the balanced equation is 4HF + 2NaOH -> 2NaF + 2H2O. Using stoichiometry, you can determine that for every 4 moles of hydrofluoric acid (HF), you produce 2 moles of sodium fluoride (NaF). Therefore, you can set up a proportion or calculation to find the mass of NaF produced.
9. The procedure that could be used to demonstrate the conservation of matter during a physical change is: Find the mass of a cup of water. Boil the water. Find the mass of the water that remains. To determine this, you need to understand the concept of conservation of matter. By measuring the mass of a substance before and after a physical change, you can demonstrate that the mass remains constant. Boiling water is a good example because the water evaporates, but the mass of the remaining water should be the same.
10. The number of atoms in the products of the given reaction is: four. To determine this, you need to understand the stoichiometry of the reaction. The equation shows that one molecule of Br2 combines with two molecules of KCl. Since each molecule of Br2 contains two atoms of bromine (Br) and each molecule of KCl contains three atoms in total (one K and one Cl), the products will contain a total of four atoms (2 Br and 2 K).
11. To balance the unbalanced chemical equation 2NaHCO3 -> Na2CO3 + CO2, the following can be added to the products as coefficients: H2O. To determine this, you need to understand how to balance chemical equations. By adjusting the coefficients in front of the compounds, you can ensure that the number of atoms on both sides of the equation is equal. In this case, you can balance the equation by adding a coefficient of 2 in front of H2O. The balanced equation will then be: 2NaHCO3 -> Na2CO3 + CO2 + H2O.
I hope this helps! Let me know if you have any more questions.
58 - 27 = 32
so yes 27 protons, 32 neutrons
I am not going to do all these for you. I do not need the practiced but you do.
Where is your work?
Believe me the teachers here have complained about the new Jiska format. We are also frustrated.
I don't see any effort on your part to answer any of these. What are your thoughts? Get out a periodic table. That will answer several just by looking at the chart.
If you lose your post, which is easy these days, just click on load more and your post will be down the list somewhere.