Answer:
- <em><u>Mendeleev produced the first orderly arrangement of known elements.</u></em>
- <em><u>Mendeleev used patterns to predict undiscovered elements.</u></em>
Explanation:
- <u>Mendeleev produced the first orderly arrangement of known elements and used patterns to predict the undiscovered elements.</u>
Those two statments are true.
For the time being there were some 62 known elements. Before Medeleev some schemes to order part of the elements were proposed, but Medeleev showed the relationship between the atomic mass and the properties of the elements (supports second choice). This arrangement is known as the periodic table.
More importantly, Mendeleev predicted correctly the existance and properties of unknown elements, which is his major contribution: he left blanket spaces which where gradually filled when new elements where discovered (this supports the fourth choice).
The first modern chemistry book was written by Antoine Lavoisier (this discards first option).
Mendeleev ordered the elements by increasing mass number (this discards third choice), which was corrected later by the scientist Henry Moseley, who ordered the elements by increasing atomic number (number of protons).
Isotopes were not known by Mendeleev times, so this discards the last option.
Answer:
When two forces are the same strength but act in opposite direction, they are called balanced forces. Again, tug-of-war is a perfect example. If the people on each side of the rope are pulling with the same strength, but in the opposite direction, the forces are balanced. The result is no motion.
Explanation:
Hope this helps!
Those would be called indicators , simply google them and you should find many. I'll leave some examples "bromophenol blue" "Methyl red" and "phenol red".
Answer:
526g is the mass of this sample
Explanation:
To solve this question we must, as first, find the <em>molar mass </em>of Al₂(Cr₂O₇)₃ using the periodic table. The molar mass is defined as the mass of this compound per mole. With this value we can find the mass in 0.750 moles as follows:
<em>Molar mass Al₂(Cr₂O₇)₃</em>
2Al = 2*26.98g/mol = 53.96g/mol
6 Cr = 6*51.9961g/mol = 311.9766g/mol
21 O = 21*15.999g/mol = 335.979g/mol
53.96g/mol + 311.9766g/mol + 335.979g/mol
= 701.9156g/mol
The mass of 0.750 moles is:
0.750 moles * (701.9156g / mol) =
<h3>526g is the mass of this sample</h3>
Stalactites and stalagmites form as ________ precipitates out of the water evaporating in underground caves.
Group of answer choices
hydrochloric acid
sodium bicarbonate
calcium carbonate
sodium chloride
sodium hydroxide
Answer:
calcium carbonate
Explanation:
A stalactite is an icicle-looking mould that is formed by the precipitation of natural minerals as a result of water dripping from the ceiling, hanging from a cave.
A stalagmites in the other hand, grows upwards and is also a mound that is formed by the deposits of minerals gotten by the water dripping on the floor of a cave.
Therefore, stalactites and stalagmites form as calcium carbonate precipitates out of the water evaporating in underground caves.
