Science plz help due soon 6th grade Major grade

If a molecule diffusing through extracellular fluid travels 1 mm in 1 sec, how long will it take that molecule to diffuse 1 cm

hichkok12 [17]

Given that the rate of diffusion is 1 mm per 1 second. then the time it travels in 1 cm can be solve using the formula
t = d / r
where d is the distance
r is the rate

first, 1 cm is equal to 10 mm

t = 10 mm / ( 1 mm / s )
t = 10 s

4 0

3 years ago

How does a small set of elements combine to form molecules , compounds and mixtures, which are used in your daily lives?

Anastaziya [24]

Elements are the simplest substances in nature that cannot be broken down into smaller parts by normal chemical means. They contain only atoms of the same type, ones that have identical chemical properties. There are at least 90 naturally-occurring elements, plus man-made ones. If you look at a periodic table, you'll see the names of each of these elements and some of their properties (such as mass, or how heavy the atom is).

Molecules & Compounds

When atoms from different elements are joined together in groups, they form molecules. The atoms in molecules bind together chemically, which means that the atoms cannot be separated again by physical means, such as filtration. The molecule has different properties from the elements from which is was made. A water molecule is not three separate atoms, two hydrogen (H) and one oxygen (O), but it is actually a unique H2O molecule with its own set of distinct properties.

Like elements that are formed of atoms of the same sort, compounds are formed of molecules of the same sort. The elements can be combined into about 2 million different compounds! Did you know that eggshells are made up of a calcium carbonate compound? And citric acid, which is found in oranges and other citrus fruit, is a compound of carbon, hydrogen, and oxygen atoms. Your kids might find it helpful to do a science research project finding other common compounds around your house. Make hypotheses and do research using a chemistry reference book, web site, or text book to find out the answers.

There are more carbon compounds than compounds of any other element. Organic compound is the name for the carbon compounds found in all living things.

Mixtures - A Bit of This and That

All matter can be classified into two categories: pure substances and mixtures. A pure substance consists of a single element or compound. Iron is formed only of iron (Fe) atoms; table salt is formed only of sodium chloride (NaCl) molecules. A mixture, however, is made up of different compounds and/or elements. When salt is added to water to make saltwater, it becomes a mixture. The salt and water molecules do not combine to form new molecules, but only "mix" together while still retaining their identities. Air is also a mixture, containing just the right amounts of nitrogen, oxygen, and other gases for life on Earth.

Not all mixtures have the same composition throughout. Salt water does, but Italian salad dressing does not--the parts separate and are not perfectly blended or homogenous. Mixtures of metals are called alloys (bronze is an alloy of copper and tin); liquid mixtures (such as saltwater) are called solutions.

The substances that make up a mixture can be separated by physical means because they have different physical properties (such as different melting points) and are not chemically bonded. A mixture can be separated into its parts in a variety of ways, including decantation (letting the sand in a mixture of water and sand settle, and then draining off the water, for example), filtering, and evaporation. You can use a kitchen funnel and coffee filter for filtration, and either use sunlight or low heat for evaporation. Try out these methods on saltwater and a sand and water mixture to see how they work and compare the results. Evaporation will work for both saltwater and sand and water solutions, but filtration will not work for saltwater. Can you think of other examples where a separating method will work for one mixture and not another? Another one to try is lemon juice, a mixture of water and citric acid; what do you think happens when it is boiled? The water evaporates and eventually leaves nothing but citric acid crystals

6 0

3 years ago

At 450°C, ammonia gas will decompose according to the following equation: 2 NH3 (g)  N2 (g) + 3 H2 (g) Kc = 4.50 at 475˚C An u

velikii [3]

Answer:

0.2024 M

Explanation:

For the decomposition reactio given, let's do an equilibrium chart. Let's call the initial concentration of NH₃ as C:

2NH₃(g) ⇄ N₂(g) + 3H₂(g)

C 0 0 Initial

-2x +x +3x Reacts (stoichiometry is 1:1:3)

C - 2x x 3x Equilibrium

3x = 0.252

x = 0.084 M

The equilibrium constant (Kc) is the multiplication of the concentrations of the products elevated by their coefficients, divided by the multiplication of reactants concentrations elevated by their coefficients.

Kc = ([H₂]³*[N₂])/([NH₃]²)

4.50 = [(0.252)³*(0.084)]/(C - 2*0.084)²

4.50 = 0.00533/(C - 0.168)²

4.50 = 0.00533/(C² - 0.336C + 0.028224)

4.50C² - 1.512C + 0.127008 = 0.00533

4.50C² - 1.512C + 0.121678 = 0

Solving the equation by a graphic calculator, for C > 0.168

C = 0.2024 M

4 0

3 years ago

Since the number of atoms in a substance is so large , a unit to count them was created. This unit is the number of atoms in 12

larisa86 [58]

The number of atoms in one mole of any substance is measured by Avogadro's number. The value of Avogadro's number is 6.023 x 10 ^23. It is named after scientist Avogadro who proposed this number. 12 grams of carbon-12 represents 1 mole of carbon-12. For this reason, the number of atoms present in 1 mole of any substance is 6.023 x 10 ^23. Therefore, the number of atoms present in 1 mole carbon-12 is 6.023 x 10^23.

(Answer) This unit is the number of atoms in 12 grams of carbon-12 and known as Avogadro's number.

7 0

3 years ago

Suppose a laboratory wants to identify an unknown pure substance. The valence electrons of the substance's atoms feel an effecti

zalisa [80]

Answer:

The answer is the third option in the list: It would have smaller atomic radii than Si and higher ionization energies than Si.

Explanation:

The effective nuclear charge is that portion of the total nuclear charge that a given electron in an atom feels.

Since, the inner electrons repel the outer electrons, the effective nuclear charge of a determined electron is the sum of the positive charge (number of protons or atomic number) that it feels from the nucleus less the number of electrons that are in the shells that are are closer to the nucleus than the own shell of such (determined) electron.

Mathematically, the effective nuclear charge (Zeff) is equal to the atomic number (Z) minus the amount (S) that other electrons in the atom shield the given (determined) atom from the nucleus.

Zeff = Z - S.

Since, the valence electrons are the electrons in the outermost shell of the atom, you can find certain trend for the value Zeff.

Let's look at the group to which Si belongs, which is the group 14. This table summarizes the relevant data:

Element Z Group # valence electrons S Zeff = Z - S

C 6 14 4 6 - 4 = 2 6 - 2 = +4

Si 14 14 4 14 - 4 = 10 14 - 10 = +4

Ge 32 14 4 32 - 4 = 28 32 -28 = +4

Sn 50 14 4 50 - 4 = 46 50 - 46 = +4

Pb 82 14 4 82 - 4 = 78 82 - 78 = +4

With that, you have shown that the valence electrons of the unknown substance's atoms feel an effective nuclear charge of +4 and you have a short list of 4 elements which can be the unknown element: C, Ge, Sn or Pb.

The second known characteristic of the unknown substance's atoms is that it has a higher electronegativity than silicon (Si).

So, you must use the known trend of the electronegativity in a group of the periodic table: the electronegativity decreases as you go down in a group. So, three of the elements (Ge, Sn, and Pb) have lower electronegativity than Si, which has left us with only one possibility: the element C. The valence electrons of carbon (C) atoms feel an effective nuclear charge of +4 and it carbon has a higher electronegativity than silicon.

Other two periodic trends attending the group number are the atomic radii and the ionization energy.

The atomic radii generally increases as you go from top to bottom in a group. This is because you are adding electrons to new higher main energy levels. So, you can conclude that the originally unknwon substance (carbon) has a smaller atomic radii, than Si.

The ionization energies generally decreases as you go from top to bottom in a group. This os due to the shielding effect: as seen, the effective nuclear charge of the atom's valence electrons remains constant, while the distance of the electrons from the nucleus increases (the valence electrons are farther away from the nucleus), which means the upper the element in a given group, the larger the ionization energy of the atoms.

With this, our conclusions about the unnkown substance are:

Since it has a higher electronegativity value than silicon (Si), it is right up of Si, and there is on only element possible element than can be (C).

Since, it is upper than silicon (Si), it would have smaller atomic radii.

Due to the shielding effect, it would have larger ionization energies.

The answer is the third option in the list: It would have smaller atomic radii than Si and higher ionization energies than Si.

6 0

2 years ago