1. Who was the first person to create a periodic table? When?

2. What is the modern periodic table?

3. Compare and contrast the periods and groups of the modern periodic table.

4. In the modern periodic table (found in the back of your agenda), find the element named lead (Pb). How many protons do atoms of lead have? To which class of elements does lead belong?

5. Most of the elements on the periodic table belong to what class of elements.

6. Which groups of the modern periodic table contain elements that are classified as metalloids?

Answer: The percent by mass concentration is 33.3 %

Explanation:

Mass percent is the ratio of mass of solute to the mass of solution in terms of percentage.

mass of solute = 50 g

mass of solution = [tex]{\text {density of solution}}\times {\text {volume of solution}}=1.5g/ml\times 1000ml=1500g[/tex]

Mass percentage = [tex]\frac{50g}{1500g}\times 100\%=33.3\%[/tex]

Thus percent by mass concentration of 1000 ml of a solution (d=1.5 g/ml) that contains 50 g of solute in it is 33.3 %

Answer:

False

Explanation:

False : It is better they are closer together

The RF ( retention factor  ) is calculated with this formula

= distance travelled / distance travelled by solvent

And the larger the RF factor of a compound the less polar the compound ( i.e. it will not stick to the stationary phase ) hence it is better the RF values of the components to be closer

Answer:

True

Explanation:

The resulting Rf factor, which has no units, is dependent upon the specific stationary and mobile phase used. Chromatogram results are considered to have better resolution if the Rf values of the components being separated are farther apart (e.g. 0.3 and 0.7) rather than closer together (e.g. 0.4 and 0.5). The distance the compound moves relative to the distance the solvent (or mobile phase or eluent) moves is a characteristic of that compound. (where Rf is equal to distance compound moved divided by solvent front distance)

Answer:

weathering and erosion

Explanation:

Sand forms when rocks break down from weathering and eroding over thousands and even millions of years. Rocks take time to decompose, especially quartz (silica) and feldspar. Often starting thousands of miles from the ocean, rocks slowly travel down rivers and streams, constantly breaking down along the way.

Answer:

weathering and erosion

Most of the matter making up earth is composed of compounds. I think

Answer:

11

Explanation:

Sodium is a chemical element with the symbol Na and atomic number 11.

Answer:

22.99g/mol (in this case 23g/mol)

Answer:

Answered below

Explanation:

>> ice is solid

>> water is liquid

>> Steam is gas

>> Ice → water = melting

>> water → steam = evaporation

>> steam → water = condensation

>> water → ice = freezing

Answer:

I think hydrogen because Hydrogen combined with one atom with oxygen and in hydrogen peroxide. It has two atoms of hydrogen and 2 atoms of oxygen. Therfore it should be a compound.

Answer: PLease see answer in explanation column

Explanation:

FIRST STEP

We  find the grams ( mass ) of solute required to prepare the solution by using  the formula

grams ( mass ) of solute, g(CaCl2)= Molar mass x Molarity of the solution x Volume of the solution

Therefore Preparing 750 mL of 1.5 M calcium chloride solution, we have that Molar mass of Calcium chloride =110.98 g/mol

g(CaCl2) =110.98 g/mol X 1.5mol/L X 0.75L

g(CaCl2) =124.8525g CaCl2

SECOND STEP

Now Dissolve 124.8525g CaCl2 in about 350ml of distilled water then add more water until the final volume be comes 750ml

Answer:

methylpentanoic acid,,,,,I guess so

The following carboxylic acid is 2-methylpentanoic acid.

A carboxylic acid is an organic compound that contains the carboxyl functional group. The general formula for a carboxylic acid can be abbreviated as R−COOH.

Pentanoic acid can be prepared by reacting a butyl halide with magnesium to obtain a Grignard reagent, which is further reacted with carbon dioxide to give valeric salt.

Hence, the following carboxylic acid is 2-methylpentanoic acid.

Learn more about the carboxylic acid here:

https://brainly.com/question/26855500

#SPJ2

Answer:

the oxidizing agent undergoes oxidation and

the reducing agent undergoes reduction simultaneously

Answer:

0.96 J/g °C

General Formulas and Concepts:

Thermochemistry

Specific Heat Formula: q = mcΔT

Explanation:

Step 1: Define

[Given] m = 5.0 g

[Given] ΔT = 22.0 °C - 20.0 °C = 2.0 °C

[Given] q = 9.6 J

[Solve] c

Step 2: Solve for c

Answer:

The dating of rocks is important because:

Explanation:

its important  to know how the rocks have changed.

Answer:

C₄H₆

Explanation:

A hydrocarbon is a molecule that only contains atoms of Carbon and Hydrogen. As you remember, the molar mass of Carbon is 12g/mol and the molar mass of Hydrogen is 1g/mol.

To solve this question we can find the amount of Carbons necessary that doesn't exceed the 54g/mol. That is:

54g/mol / 12g/mol = 4.5

As the molecular formula must be given in whole numbers, the amount of Carbons is 4. This 4 carbons have a mass of:

12g/mol*4 = 48g/mol

And the hydrogens necessaries to suply the molecular mass are:

54 - 48 = 6 hydrogens

That means molecular formula is:

Answer:

The number of atoms of each kind is indicated by a subscript following the atom. If there is only one atom, no number is written. If there is more than one atom of a specific kind, the number is written as a subscript following the atom.

Answer:

Oxidation state] is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules:

The oxidation state of a free element (uncombined element) is zero for a simple (monoatomic) ion, the oxidation state is equal to the net charge on the ion.

Hydrogen has an oxidation state of 1 and oxygen has an oxidation state of −2 when they are present in most compounds. (Exceptions to this are that hydrogen has an oxidation state of −1 in hydrides of active metals, e.g. LiH, and oxygen has an oxidation state of −1 in peroxides, e.g. H2O2 the algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion.

The same is written in my textbook. But how am I supposed to find the ox. number of an atom, which is in compound like K2UO4?

Answer: 6.75 moles of [tex]Na_2O[/tex] can be produced from 13.5 moles Na

Explanation:

The balanced chemical equation  for formation of [tex]Na_2O[/tex] from Na is:

[tex]4Na+O_2\rightarrow 2Na_2O[/tex]  

According to stoichiometry :

4 moles of Na give = 2 moles of [tex]Na_2O[/tex]

Thus 13.5 moles of [tex]Na[/tex] give =[tex]\frac{2}{4}\times 13.5=6.75moles[/tex]  of [tex]Na_2O[/tex]  

Thus 6.75 moles of [tex]Na_2O[/tex] can be produced from 13.5 moles Na

Answer:

(1) Nuclear reactions entail a transition in the nucleus of an atom, which normally results in the formation of a new substance. Chemical reactions, on the other hand, only involve electron rearrangement and do not involve nuclei modifications. (4) Nuclear reactions are unaffected by the element's chemical form.

Explanation:

Hope this helps!

Please mark me as Brainlinieast.

Answer:

a atoms

Explanation:

Answer:

C. 8.55 atoms

Explanation:

Answer:

Of course the answer is gold

Explanation:

Gold is used for making jewellery and not aluminium,iron or copper

Answer:

copper or gold.

Explanation:

Copper is also a good material for accessories. Even in the ancient times, those who can’t afford gold jewelry wear copper jewelry instead. It offers design flexibility too due to its high ductility.

Answer: pls mark brainliest

Explanation: i think so its D

Answer:

A pure substance is a substance or an element whose impurities are extracted by concentration by chemical means.

e.g Aluminium is made pure by concentration of it's ore, bauxite by treatment with excess Sodium Hydroxide solution.

Answer:

[tex]100 \times 13.5 = ikw n bahaa[/tex]

IKAW na mag tayms

Answer:

pH = 6.999

The solution is acidic.

Explanation:

HBr is a strong acid, a very strong one.

In water, this acid is totally dissociated.

HBr + H₂O  →  H₃O⁺  +  Br⁻

We can think pH, as - log 7.75×10⁻¹² but this is 11.1

acid pH can't never be higher than 7.

We apply the charge balance:

[H⁺] = [Br⁻] + [OH⁻]

All the protons come from the bromide and the OH⁻ that come from water.

We can also think [OH⁻] = Kw / [H⁺] so:

[H⁺] = [Br⁻] + Kw / [H⁺]

Now, our unknown is [H⁺]

[H⁺] =  7.75×10⁻¹² + 1×10⁻¹⁴ / [H⁺]

[H⁺] = (7.75×10⁻¹² [H⁺] + 1×10⁻¹⁴) /  [H⁺]

This is quadratic equation:  [H⁺]² - 7.75×10⁻¹² [H⁺] - 1×10⁻¹⁴

a = 1 ; b = - 7.75×10⁻¹² ; c = -1×10⁻¹⁴

(-b +- √(b² - 4ac) / (2a)

[H⁺] = 1.000038751×10⁻⁷

- log [H⁺] = pH → 6.999

A very strong acid as HBr, in this case, it is so diluted that its pH is almost neutral.

Answer:

Na2SO4

Explanation:

Na2SO4 dissociates completely in solution to yield ions therefore it is the strongest electrolyte.

The question is incomplete as the table is missing but I will try to explain as generally as possible. Recall that an electrolyte is a compound that conducts electricity in solution.

Also recall that the number of ions available in solution determines the electrolytic strength of a substance. Hence, Na2SO4 dissociates completely in solution to yield ions therefore it is the strongest electrolyte.

Learn more about electrolytes: https://brainly.com/question/1301963

Answer:

D The atom gains an electron in an oxidation-reduction reaction.

Answer:

Bonds are polar when one element in a compound is more electronegative than the other. This creates a dipole in the molecule where one end of the molecule is partially positive and one end is partially negative

Explanation:

Answer:

30.26 grams of N₂O₃

Explanation:

Divide by Avogadro's number. This leaves you with the number of moles. Then, multiply by the molar mass of N₂O₃